​FLOWER (Lat. flos, floris; Fr. fleur), a term popularly used for the bloom or blossom of a plant, and so by analogy for the fairest, choicest or finest part or aspect of anything, and in various technical senses. Here we shall deal only with its botanical interest. It is impossible to give a rigid botanical definition of the term “flower.” The flower is a characteristic feature of the highest group of the plant kingdom—the flowering plants (Phanerogams)—and is the name given to the association of organs, more or less leaf-like in form, which are concerned with the production of the fruit or seed. In modern botanical works the group is often known as the seed-plants (Spermatophyta). As the seed develops from the ovule which has been fertilized by the pollen, the essential structures for seed-production are two, viz. the pollen-bearer or stamen and the ovule-bearer or carpel. These are with few exceptions foliar structures, known in comparative morphology as sporophylls, because they bear the spores, namely, the microspores or pollen-grains which are developed in the microsporangia or pollen-sacs, and the mega spore, which is contained in the ovule or megasporangium.

In Gymnosperms (q.v.), which represent the more primitive ​type of seed-plants, the micro- or macro-sporophylls are generally
associated, often in large numbers, in separate cones, to which
the term “flower” has been applied. But there is considerable
difference of opinion as to the relation between these cones
and the more definite and elaborate structure known as the
flower in the higher group of seed-plants—the Angiosperms (q.v.)—and
it is to this more definite structure that we generally refer
in using the term “flower.”

Fig. 1.—Proliferous Rose.

s,

Sepals transformed into leaves.

p,

Petals multiplied at the expense of the stamens, which are reduced in number.

c,

Coloured leaves representing abortive carpels.

a,

Axis prolonged, bearing an imperfect flower at its apex.

Flowers are produced from flower-buds, just as leaf-shoots
arise from leaf-buds. These two kinds of buds have a resemblance
to each other as regards the arrangement and the development
of their parts; and it sometimes happens, from injury and
other causes, that the part of the axis which, in ordinary cases,
would produce a leaf-bud, gives origin to a flower-bud. A
flower-bud has not in ordinary circumstances any power of
extension by the continuous development
of its apex. In this
respect it differs from a leaf-bud.
In some cases, however, of monstrosity,
especially seen in the rose
(fig. 1), the central part is prolonged,
and bears leaves or flowers.
In such cases the flowers, so far as
their functional capabilities are
concerned, are usually abortive.
This phenomenon is known as proliferation
of the floral axis.

Flower-buds, like leaf-buds, are
produced in the axil of leaves,
which are called bracts.

The term bract is properly applied
to the leaf from which the primary
floral axis, whether
simple or branched,
arises, while the leaves which arise
on the axis between the bract and
the outer envelope of the flower
Bracts.
are bracteoles or bractlets. Bracts
sometimes do not differ from
the ordinary leaves, as in Veronica
hederifolia, Vinca, Anagallis andAjuga. In general as regards their
form and appearance they differ
from ordinary leaves, the difference
being greater in the upper than
in the lower branches of an inflorescence.
They are distinguished
by their position at the base of
the flower or flower-stalk. Their
arrangement is similar to that of
the leaves. When the flower is sessile the bracts are often
applied closely to the calyx, and may thus be confounded with
it, as in the order Malvaceae and species of Dianthus and winter
aconite (Eranthis), where they have received the name of epicalyx
or calyculus. In some Rosaceous plants an epicalyx is present,
due to the formation of stipulary structures by the sepals. In
many cases bracts act as protective organs, within or beneath
which the young flowers are concealed in their earliest stage of
growth.

When bracts become coloured, as in Amherstia nobilis,
Euphorbia splendens, Erica elegans and Salvia splendens, they
may be mistaken for parts of the corolla. They are sometimes
mere scales or threads, and at other times are undeveloped,
giving rise to the ebracteate inflorescence of Cruciferae and some
Boraginaceae. Sometimes they are empty, no flower-buds
being produced in their axil. A series of empty coloured bracts
terminates the inflorescence of Salvia Horminum. The smaller
bracts or bracteoles, which occur among the subdivisions of a
branching inflorescence, often produce no flower-buds, and thus
anomalies occur in the floral arrangements. Bracts are occasionally
persistent, remaining long attached to the base of the
peduncles, but more usually they are deciduous, falling off early
by an articulation. In some instances they form part of the
fruit, becoming incorporated with other organs. Thus, the cones
of firs and the stroboli of the hop are composed of a series of
spirally arranged bracts covering fertile flowers; and the scales
on the fruit of the pine-apple are of the same nature. At the
base of the general umbel in umbelliferous plants a whorl of
bracts often exists, called a general involucre, and at the base
of the smaller umbels or umbellules there is a similar leafy whorl
called an involucel or partial involucre. In some instances, as in
fool’s-parsley, there is no general involucre, but simply an
involucel; while in other cases, as in fennel or dill (fig. 15),
neither involucre nor involucel is developed. In Compositae
the name involucre is applied to the bracts surrounding the head
of flowers (fig. 2, i), as in marigold, dandelion, daisy, artichoke.
This involucre is frequently composed of several rows of leaflets,
which are either of the same or of different forms and lengths,
and often lie over each other in an imbricated manner. The
leaves of the involucre are spiny in thistles and in teazel (Dipsacus),
and hooked in burdock. Such whorled or verticillate
bracts generally remain separate (polyphyllous), but may be
united by cohesion (gamophyllous), as in many species of Bupleurum
and in Lavatera. In Compositae besides the involucre
there are frequently chaffy and setose bracts at the base of each
flower, and in Dipsacaceae a membranous tube surrounds each
flower. These structures are of the nature of an epicalyx. In
the acorn the cupule or cup (fig. 3) is formed by a growing
upwards of the flower-stalk immediately beneath the flower,
upon which scaly or spiny protuberances appear; it is of the
nature of bracts. Bracts also compose the husky covering of
the hazel-nut.

Fig. 2.—Head (capitulum) of
Marigold (Calendula), showing
a congeries of flowers, enclosed
by rows of bracts, i, at the base,
which are collectively called an
involucre.

From Strasburger’s Lehrbuch der Botanik,
by permission of Gustav Fischer.

When bracts become united, and overlie each other in several
rows, it often happens that the outer ones do not produce flowers,
that is, are empty or sterile. In the artichoke the outer imbricated
scales or bracts are in this condition, and it is from the
membranous white scales or bracts (paleae) forming the choke
attached to the edible receptacle that the flowers are produced.
The sterile bracts of the daisy occasionally produce capitula,
and give rise to the hen-and-chickens daisy. In place of developing
flower-buds, bracts may, in certain circumstances, as in
proliferous or viviparous plants, produce leaf-buds.

A sheathing bract enclosing one or several flowers is called
a spathe. It is common among Monocotyledons, as Narcissus
(fig. 4), snow-flake, Arum and palms. In some palms it is 20
ft. long, and encloses 200,000 flowers. It is often associated
with that form of inflorescence termed the spadix, and may be
coloured, as in Anthurium, or white, as in arum lily (Richardiaaethiopica). When the spadix is compound or branching, as in
palms, there are smaller spathes, surrounding separate parts of
the inflorescence. The spathe protects the flowers in their young
state, and often falls off after they are developed, or hangs down ​in a withered form, as in some palms, Typha and Pothos. In
grasses the outer scales or glumes of the spikelets are sterile
bracts (fig. 5, gl); and in Cyperaceae bracts enclose the organs
of reproduction. Bracts are
frequently changed into complete
leaves. This change is
called phyllody of bracts, and
is seen in species of Plantago,
especially in the variety of
Plantago media, called the
rose-plantain in gardens,
where the bracts become leafy
and form a rosette round the
flowering axis. Similar changes
occur in Plantago major, P.
lanceolata, Ajuga reptans,
dandelion, daisy, dahlia and
in umbelliferous plants. The
conversion of bracts into
stamens (staminody of bracts)
has been observed in the case
of Abies excelsa. A lengthening
of the axis of the female
strobilus of Coniferae is not
of infrequent occurrence in
Cryptomeria japonica, larch (Larix europaea), &c., and this is
usually associated with a leaf-like condition of the bracts, and
sometimes even with
the development of
leaf-bearing shoots in
place of the scales.

The arrangement of
the flowers on the axis,
or the ramification of
the floral axis, is called
the inflorescence. The
primary axis of the
inflorescence is sometimes
called the rachis;
its branches, whether
terminal or lateral,
which form the stalks
supporting flowers or
clusters of flowers, are
peduncles, and if small
branches are given off
by it, they are called
pedicels. A flower
having a stalk is called
pedunculate or pedicellate;
one having no stalk is sessile. In describing a branching
inflorescence, it is common to speak of the rachis as the primary
floral axis, its branches as the secondary floral axes, their divisions
as the tertiary floral axes,
and so on; thus avoiding any
confusion that might arise from
the use of the terms rachis, peduncle
and pedicel.

The peduncle is simple, bearing
a single flower, as in primrose;
or branched, as in London-pride.
It is sometimes succulent, as in
the cashew, in which it forms the
large coloured expansion supporting
the nut; spiral, as in
Cyclamen and Vallisneria; or
spiny, as in Alyssum spinosum. When the peduncle proceeds
from radical leaves, that is, from an axis which is so shortened
as to bring the leaves close together in the form of a cluster, as
in the primrose, auricula or hyacinth, it is termed a scape.
The floral axis may be shortened, assuming a flattened, convex
or concave form, and bearing numerous flowers, as in the artichoke,
daisy and fig (fig. 6). The floral axis sometimes appears as
if formed by several peduncles
united together, constituting a
fasciated axis, as in the cockscomb,
in which the flowers form
a peculiar crest at the apex of
the flattened peduncles. Adhesions
occasionally take place
between the peduncle and the
bracts or leaves of the plant, as
in the lime-tree (fig. 7). The
adhesion of the peduncles to the
stem accounts for the extra-axillary
position of flowers, as
in many Solanaceae. When this
union extends for a considerable
length along the stem, several
leaves may be interposed between
the part where the peduncle
becomes free and the leaf
whence it originated, and it may
be difficult to trace the connexion.
The peduncle occasionally
becomes abortive, and in
place of bearing a flower, is transformed
into a tendril; at other
times it is hollowed at the apex,
so as apparently to form the
lower part of the outer whorl of
floral leaves as in Eschscholtzia.
The termination of the peduncle,
or the part on which the whorls
of the flower are arranged, is
called the thalamus, torus or receptacle.

Fig. 9.—Head of flowers (capitulum)
of Scabiosa atropurpurea. The inflorescence
is simple and indeterminate,
and the expansion of the flowers centripetal,
those at the circumference
opening first.

There are two distinct types of
inflorescence—one in which the
flowers arise as lateral shoots
from a primary axis, which goes
on elongating, and the lateral
shoots never exceed in their development the length of the
Inflorescence.
primary axis beyond their
point of origin. The flowers
are thus always axillary.
Exceptions, such as in cruciferous
plants, are due to the non-appearance
of the bracts. In the other
type the primary axis terminates
in a single flower, but lateral axes are
given off from the axils of the bracts,
which again repeat the primary axis;
the development of each lateral axis
is stronger than that of the primary
axis beyond its point of origin. The
flowers produced in this inflorescence
are thus terminal. The first kind
of inflorescence is indeterminate,
indefinite or axillary. Here the axis is either elongated, ​producing flower-buds as it grows, the lower expanding first
(fig. 8), or it is shortened and depressed, and the outer flowers
expand first (fig. 9). The expansion of the flowers is thus
centripetal, that is, from base to apex, or from circumference
to centre.

The second kind of inflorescence is determinate, definite or
terminal. In this the axis is either elongated and ends in a solitary
flower, which thus terminates the axis, and if other flowers are
produced, they belong to secondary axes farther from the centre;
or the axis is shortened and flattened,
producing a number of
separate floral axes, the central
one expanding first, while the
others are developed in succession
farther from the centre. The expansion
of the flowers is in this
case centrifugal, that is, from apex
to base, or from centre to circumference.
It is illustrated in fig. 10,
Ranunculus bulbosus; a′ is the
primary axis swollen at the base in
a bulb-like manner b, and with
roots proceeding from it. From
the leaves which are radical proceeds
the axis ending in a solitary
terminal flower f′. About the
middle of this axis there is a leaf
or bract, from which a secondary
floral axis a″ is produced, ending
in a single flower f″, less advanced
than the flower f′. This secondary
axis bears a leaf also, from which
a tertiary floral axis a″′ is produced,
bearing an unexpanded solitary flower f″′. From this
tertiary axis a fourth is in progress of formation. Here f′ is the
termination of the primary axis, and this flower expands first,
while the other flowers are developed centrifugally on separate
axes.

A third series of inflorescences, termed mixed, may be recognized.
In them the primary axis has an arrangement belonging
to the opposite type from that of the branches, or vice versa.
According to the mode and degree of development of the lateral
shoots and also of the bracts, various forms of both inflorescences
result.

Fig. 11.—Corymb of Cerasus Mahaleb, terminating an abortive
branch, at the base of which are modified leaves in the form of scales,
e. a′, Primary axis; a″, secondary axes bearing flowers; b, bract in
the axils of which the secondary axes arise.

Fig. 12.—Spike of Vervain (Verbena officinalis), showing sessile
flowers on a common rachis. The flowers at the lower part of the
spike have passed into fruit, those towards the middle are in full
bloom, and those at the top are only in bud.

Fig. 13.—Amentum or catkin of Hazel (Corylus Avellana), consisting
of an axis or rachis covered with bracts in the form of scales,
each of which covers a male flower, the stamens of which are seen
projecting beyond the scale. The catkin falls off in a mass, separating
from the branch by an articulation.

Amongst indefinite forms the simplest occurs when a lateral
shoot produced in the axil of a large single foliage leaf of the plant
ends in a single flower, the axis of the plant elongating beyond,
as in Veronica hederifolia, Vinca minor and Lysimachia nemorum.
The flower in this case is solitary, and the ordinary leaves become
bracts by producing flower-buds in place of leaf-buds; their
number, like that of the leaves of this main axis, is indefinite,
varying with the vigour of the plant. Usually, however, the
floral axis, arising from a more or less altered leaf or bract,
instead of ending in a solitary flower, is prolonged, and bears
numerous bracteoles, from which smaller peduncles are produced,
and those again in their turn may be branched in a similar way.
Thus the flowers are arranged in groups, and frequently very
complicated forms of inflorescence result. When the primary
peduncle or floral axis, as in fig. 8, is elongated, and gives off
pedicels, ending in single flowers, a raceme is produced, as in
currant, hyacinth and barberry. If the secondary floral axes
give rise to tertiary ones, the raceme is branching, and forms a
panicle, as in Yucca gloriosa. If in a raceme the lower flower-stalks
are developed more strongly than the upper, and thus all
the flowers are nearly on a level, a corymb is formed, which may be
simple, as in fig. 11, where the primary axis a′ gives off secondary
axes a″, a″, which end in single flowers; or branching, where
the secondary axes again subdivide. If the pedicels are very short
or wanting, so that the flowers are sessile, a spike is produced, as
in Plantago and vervain (Verbena officinalis) (fig. 12). If the
spike bears unisexual flowers, as in willow or hazel (fig. 13), it is an
amentum or catkin, hence such trees are called amentiferous; at
other times it becomes succulent, bearing numerous flowers,
surrounded by a sheathing bract or spathe, and then it constitutes
a spadix, which may be simple, as in Arum maculatum (fig. 14),
or branching as in palms. A spike bearing female flowers only,
and covered with scales, is a strobilus, as in the hop. In grasses
there are usually numerous sessile flowers arranged in small
spikes, called locustae or spikelets, which are either set closely
along a central axis, or produced on secondary axes formed by
the branching of the central one; to the latter form the term
panicle is applied.

Fig. 15.—Compound umbel of Common
Dill (Anethum graveolens), having
a primary umbel a, and secondary
umbels b, without either involucre or
involucel.

If the primary axis, in place of being elongated, is contracted,
it gives rise to other forms of indefinite inflorescence. When the
axis is so shortened that the secondary axes arise from a common
point, and spread out as radii of nearly equal length, each ending
in a single flower or dividing again in a similar radiating manner,
an umbel is produced, as in fig. 15. From the primary floral
axis a the secondary axes come off in a radiating or umbrella-like
manner, and end in small umbels b, which are called partialumbels or umbellules. This inflorescence is seen in hemlock and
other allied plants, which are hence called umbelliferous. If
there are numerous flowers on a flattened, convex or slightly
concave receptacle, having either very short pedicels or none, a ​capitulum (head) is formed, as in dandelion, daisy and other
composite plants (fig. 2), also in scabious (fig. 9) and teazel.
In the American button-bush the heads are globular, in some
species of teazel elliptical, while in scabious and in composite
plants, as sunflower, dandelion, thistle, centaury and marigold,
they are somewhat hemispherical, with a flattened, slightly
hollowed, or convex disk. If the margins of such a receptacle
be developed upwards, the centre not developing, a concave
receptacle is formed, which may partially or completely enclose
a number of flowers that are generally unisexual. This gives rise
to the peculiar inflorescence of Dorstenia, or to that of the fig
(fig. 6), where the flowers are placed on the inner surface of the
hollow receptacle, and are provided with bracteoles. This inflorescence
has been called a hypanthodium.

Lastly, we have what are called compound indefinite inflorescences.
In these forms the lateral shoots, developed centripetally
upon the primary axis, bear numerous bracteoles, from which
floral shoots arise which may have a centripetal arrangement
similar to that on the mother shoot, or it may be different. Thus
we may have a group of racemes, arranged in a racemose manner
on a common axis, forming a raceme of racemes or compound
raceme, as in Astilbe. In the same way we may have compound
umbels, as in hemlock and most Umbelliferae (fig. 15), a compound
spike, as in rye-grass, a compound spadix, as in some
palms, and a compound capitulum, as in the hen-and-chickens
daisy. Again, there may be a raceme of capitula, that is, a group
of capitula disposed in a racemose manner, as in Petasites, a
raceme of umbels, as in ivy, and so on, all the forms of inflorescence
being indefinite in disposition. In Eryngium the shortening
of the pedicels changes an umbel into a capitulum.

The simplest form of the definite type of the inflorescence is
seen in Anemone nemorosa and in gentianella (Gentiana acaulis),
where the axis terminates in a single flower, no other flowers
being produced upon the plant. This is a solitary terminal
inflorescence. If other flowers were produced, they would arise
as lateral shoots from the bracts below the first-formed flower.
The general name of cyme is applied to the arrangement of a
group of flowers in a definite inflorescence. A cymose inflorescence
is an inflorescence where the primary floral axis before
terminating in a flower gives off one or more lateral unifloral
axes which repeat the process—the development being only
limited by the vigour of the plant. The floral axes are thus
centrifugally developed. The cyme, according to its development,
has been characterized as biparous or uniparous. In fig. 16
the biparous cyme is represented in the flowering branch of
Cerastium. Here the primary axis t ends in a flower, which has
passed into the state of fruit. At its base two leaves are produced,
in each of which arise secondary axes t′t′, ending in single flowers,
and at the base of these axes a pair of opposite leaves is produced,
giving rise to tertiary axes t″t″, ending in single flowers, and
so on. The term dichasium has also been applied to this form
of cyme.

In the natural order Carophyllaceae (pink family) the dichasial
form of inflorescence is very general. In some members of the
order, as Dianthus barbatus, D. carthusianorum, &c., in which
the peduncles are short, and the flowers closely approximated,
with a centrifugal expansion, the inflorescence has the form of a
contracted dichasium, and receives the name of fascicle. When
the axes become very much shortened, the arrangement is more
complicated in appearance, and the nature of the inflorescence
can only be recognized by the order of opening of the flowers.
In Labiate plants, as the dead-nettle (Lamium), the flowers are
produced in the axil of each of the foliage leaves of the plant,
and they appear as if arranged in a simple whorl of flowers.
But on examination it is found that there is a central flower
expanding first, and from its axis two secondary axes spring
bearing solitary flowers; the expansion is thus centrifugal.
The inflorescence is therefore a contracted dichasium, the flowers
being sessile, or nearly so, and the clusters are called verticillasters
(fig. 17). Sometimes, especially towards the summit of a dichasium,
owing to the exhaustion of the growing power of the
plant, only one of the bracts gives origin to a new axis, the other
remaining empty; thus the inflorescence becomes unilateral,
and further development is arrested. In addition to the dichasial
form there are others where more than two lateral axes are
produced from the primary floral axis, each of which in turn
produces numerous axes. To this form the terms trichasial and
polychasial cyme have been applied; but these are now usually
designated cymose umbels. They are well seen in some species
of Euphorbia. Another term, anthela, has been used to distinguish
such forms as occur in several species of Luzula and
Juncus, where numerous lateral axes arising from the primary
axis grow very strongly and develop in an irregular manner.

Fig. 17.—Flowering stalk of the White Dead-nettle (Lamiumalbum). The bracts are like the ordinary leaves of the plant, and
produce clusters of flowers in their axil. The clusters are called
verticillasters, and consist of flowers which are produced in a centrifugal
manner.

In the uniparous cyme a number of floral axes are successively
developed one from the other, but the axis of each successive
generation, instead of producing a pair of bracts, produces only
one. The basal portion of the consecutive axes may become
much thickened and arranged more or less in a straight line, ​and thus collectively form an apparent or false axis or sympodium,
and the inflorescence thus simulates a raceme. In the true
raceme, however, we find only a single axis, producing in succession
a series of bracts, from which the floral peduncles arise as
lateral shoots, and thus each flower is on the same side of the
floral axis as the bract in the axil of which it is developed; but
in the uniparous cyme the flower of each of these axes, the basal
portions of which unite to form the false axis, is situated on the
opposite side of the axis to the bract from which it apparently
arises (fig. 18). The bract is not, however, the one from which
the axis terminating in the flower arises, but is a bract produced
upon it, and gives origin in its axil to a new axis, the basal portion
of which, constituting the next part of the false axis, occupies
the angle between this bract and its parent axis—the bract
from which the axis really does arise being situated lower down
upon the same side of the axis with itself. The uniparous cyme
presents two forms, the scorpioid or cicinal and the helicoid or
bostrychoid.

Fig. 18.

Fig. 19.

⁠

Fig. 20.

Fig. 21.

Fig. 18.—Helicoid cyme of a species of Alstroemeria. a1, a2, a3, a4,
&c., separate axes successively developed in the axils of the corresponding
bracts b2, b3, b4, &c., and ending in a flower f2, f3, f4, &c. The
whole appears to form a simple raceme of which the axes form the
internodes.

Fig. 21.—Flowering stalk of Ragwort (Senecio). The flowers are
in heads (capitula), and open from the circumference inwards in an
indefinite centripetal manner. The heads of flowers, on the other
hand, taken collectively, expand centrifugally—the central one a
first.

In the scorpioid cyme the flowers are arranged alternately in a
double row along one side of the false axis (fig. 19), the bracts
when developed forming a second double row on the opposite
side; the whole inflorescence usually curves on itself like a
scorpion’s tail, hence its name. In fig. 20 is shown a diagrammatic
sketch of this arrangement. The false axis, a b c d, is
formed by successive generations of unifloral axes, the flowers
being arranged along one side alternately and in a double row;
had the bracts been developed they would have formed a similar
double row on the opposite side of the false axis; the whole
inflorescence is represented as curved on itself. The inflorescence
in the family Boraginaceae are usually regarded as true scorpioid
cymes.

In the helicoid cyme there is also a false axis formed by the
basal portion of the separate axes, but the flowers are not placed
in a double row, but in a single row, and form a spiral or helix
round the false axis. In Alstroemeria, as represented in fig. 18,
the axis a1 ends in a flower (cut off in the figure) and bears a leaf.
From the axil of this leaf, that is, between it and the primary
axis a1 arises a secondary axis a2, ending in a flower f2, and
producing a leaf about the middle. From the axil of this leaf
a tertiary floral axis a3, ending in a flower f3, takes origin.
In this case the axes are not arranged in two rows along one
side of the false axis, but are placed at regular intervals, so as
to form an elongated spiral round it.

Compound definite inflorescences are by no means common,
but in Streptocarpus polyanthus and in several calceolarias
we probably have examples. Here there are scorpioid cymes ofpairs of flowers, each pair consisting of an older and a younger
flower.

Forms of inflorescence occur, in which both the definite
and indefinite types are represented—mixed inflorescences.
Thus in Composite plants, such as hawk weeds (Hieracia)
and ragworts (Senecio, fig. 21), the heads of flowers,
Mixed inflorescence.
taken as a whole, are developed centrifugally, the
terminal head first, while the florets, or small flowers
on the receptacle, open centripetally, those at the circumference
first. So also in Labiatae, such as dead-nettle (Lamium), the
different whorls of inflorescence are developed centripetally,
while the florets of the verticillaster are centrifugal. This mixed
character presents difficulties in such cases as Labiatae, where
the leaves, in place of retaining their ordinary form, become
bracts, and thus might lead to the supposition of the whole
series of flowers being one inflorescence. In such cases the cymes
are described as spiked, racemose, or panicled, according to
circumstances. In Saxifraga umbrosa (London-pride) and in
the horse-chestnut we meet with a raceme of scorpioid cymes;
in sea-pink, a capitulum of contracted scorpioid cymes (often
called a glomerulus); in laurustinus, a compound umbel of
dichasial cymes; a scorpioid cyme of capitula in Vernoniascorpioides. The so-called catkins of the birch are, in reality,
spikes of contracted dichasial cymes. In the bell-flower (Campanula)
there is a racemose uniparous cyme. In the privet
(Ligustrum vulgare) there are numerous racemes of dichasia
arranged in a racemose manner along an axis; the whole inflorescence
thus has an appearance not unlike a bunch of grapes,
and has been called a thyrsus.

Fig. 23.—Diagram of a completely
symmetrical flower, consisting
of four whorls, each of
five parts, s, Sepals; p, petals;
a, stamens; c, carpels.

Fig. 24.—Monochlamydeous
(apetalous) flower of Goosefoot
(Chenopodium), consisting
of a single perianth (calyx) of five
parts, enclosing five stamens,
which are opposite the divisions
of the perianth, owing to the
absence of the petals.

Fig. 25.—Stamen, consisting
of a filament (stalk) f and an
anther a, containing the pollen p,
which is discharged through slits
in the two lobes of the anther.

Fig. 26.—The pistil of Tobacco
(Nicotiana Tabacum), consisting
of the ovary o, containing
ovules, the style s, and the
capitate stigma g. The pistil is
placed on the receptacle r, at the
extremity of the peduncle.

The flower consists of the floral axis bearing the sporophylls
(stamens and carpels), usually with certain protective envelopes.
The axis is usually very much
contracted, no internodes
being developed,
and the portion
bearing the floral leaves, termed
The flower.
the thalamus or torus, frequently
expands into a conical, flattened
or hollowed expansion; at other
times, though rarely, the internodes
are developed and it is
elongated. Upon this torus the
parts of the flower are arranged
in a crowded manner, usually
forming a series of verticils, the
parts of which alternate; but
they are sometimes arranged
spirally especially if the floral
axis be elongated. In a typical
flower, as in fig. 22, we recognize
four distinct whorls of leaves:
an outer whorl, the calyx of
sepals; within it, another whorl,
the parts alternating with those
of the outer whorl, the corolla of
petals; next a whorl of parts
alternating with the parts of
the corolla, the androecium of
stamens; and in the centre the
gynoecium of carpels. Fig. 23 is
a diagrammatic representation
of the arrangement of the parts
of such a flower; it is known as
a floral diagram. The flower is
supposed to be cut transversely,
and the parts of each whorl
are distinguished by a different
symbol. Of these whorls the
two internal, forming the sporophylls,
constitute the essential
organs of reproduction; the two
outer whorls are the protective
coverings or floral envelopes. The
sepals are generally of a greenish
colour; their function is mainly
protective, shielding the more
delicate internal organs before
the flower opens. The petals are
usually showy, and normally
alternate with the sepals. Sometimes,
as usually in monocotyledons,
the calyx and corolla are
similar; in such cases the term
perianth, or perigone, is applied.
Thus, in the tulip, crocus, lily,
hyacinth, we speak of the parts of the perianth, in place of
calyx and corolla, although in these plants there is an outer
whorl (calyx), of three parts, and an inner (corolla), of a
similar number, alternating with them. When the parts of
the calyx are in appearance like petals they are said to be
petaloid, as in Liliaceae. In some cases the petals have the
appearance of sepals, then they are sepaloid, as in Juncaceae.
In plants, as Nymphaea alba, where a spiral arrangement of the
floral leaves occurs, it is not easy to say where the calyx ends
and the corolla begins, as these two whorls pass insensibly into
each other. When both calyx and corolla are present, the plants
are dichlamydeous; when one only is present, the flower is
termed monochlamydeous or apetalous, having no petals (fig. 24).
Sometimes both are absent, when the flower is achlamydeous,
or naked, as in willow. The outermost series of the essential
organs, collectively termed the androecium, is composed of the
microsporophylls known as the staminal leaves or stamens. In
their most differentiated form each consists of a stalk, the
filament (fig. 25, f), supporting at its summit the anther
(a), consisting of the pollen-sacs which contain the powdery
pollen (p), the microspores, which is ultimately discharged
therefrom. The gynoecium or pistil is the central portion
of the flower, terminating the floral axis. It consists of one
or more carpels (megasporophylls), either separate (fig. 22, c)
or combined (fig. 24). The parts distinguished in the pistil
are the ovary (fig. 26, o), which is the lower portion enclosing
the ovules destined to become seeds, and the stigma (g), a portion
of loose cellular tissue, the receptive surface on which the pollen
is deposited, which is either sessile on the apex of the ovary,
as in the poppy, or is separated from it by a prolonged portion
called the style (s). The androecium and gynoecium are not
present in all flowers. When both are present the flower is
hermaphrodite; and in descriptive botany such a flower is
indicated by the symbol ☿. When only one of those organs
is present the flower is unisexual or diclinous, and is either male
(staminate), ♁; or female (pistillate), ♀. A flower then normally
consists of the four series of leaves—calyx, corolla, androecium
and gynoecium—and when these are all present the flower is
complete. These are usually densely crowded
upon the thalamus, but in some instances,
after apical growth has ceased in the axis,
an elongation of portions of the receptacle
by intercalary growth occurs, by which
changes in the position of the parts may be
brought about. Thus in Lychnis an elongation
of the axis betwixt the calyx and the
corolla takes place, and in this way they are
separated by an interval. Again, in the
passion-flower (Passiflora) the stamens are
separated from the corolla by an elongated
portion of the axis, which has consequently
been termed the androphore, and in Passiflora
also, fraxinella (fig. 27), Capparidaceae,
and some other plants, the ovary is
raised upon a distinct stalk termed the
gynophore; it is thus separated from the
stamens, and is said to be stipitate. Usually
the successive whorls of the flower, disposed
from below upwards or from without inwards
upon the floral axis, are of the same number of parts, or
are a multiple of the same number of parts, those of one whorl
alternating with those of the whorls next it.

Fig. 27.—Calyx
and pistil of Fraxinella
(DictamnusFraxinella). The
pistil consists of
several carpels,
which are elevated
on a stalk or gynophore
prolonged
from the receptacle.

In the more primitive types of flowers the torus is more or
less convex, and the series of organs follow in regular succession,
culminating in the carpels, in the formation of which the growth
of the axis is closed (fig. 28). This arrangement is known as
hypogynous, the other series (calyx, corolla and stamens) being
beneath (hypo-) the gynoecium. In other cases, the apex of the
growing point ceases to develop, and the parts below form a cup
around it, from the rim of which the outer members of the flower
are developed around (peri-) the carpels, which are formed from
the apex of the growing-point at the bottom of the cup. This
arrangement is known as perigynous (fig. 29). In many cases
this is carried farther and a cavity is formed which is roofed over ​by the carpels, so that the outer members of the flower spring
from the edge of the receptacle which is immediately above the
ovary (epigynous), hence the term epigyny (fig. 30).

When a flower consists of parts arranged in whorls it is said
to be cyclic, and if all the whorls have an equal number of parts
and are alternate it is eucyclic (figs. 22, 23). In
contrast to the cyclic flowers are those, as in Magnoliaceae,
Symmetry of the flower.
where the parts are in spirals (acyclic). Flowers
which are cyclic at one portion and spiral at another,
as in many Ranunculaceae, are termed hemicyclic. In spiral
flowers the distinction into series is by no means easy, and usually
there is a gradual passage from sepaloid through petaloid to
staminal parts, as in the water-lily family, Nymphaeaceae (figs.
31, 32), although in some plants there is no such distinction, the
parts being all petaloid, as in Trollius. Normally, the parts of
successive whorls alternate; but in some cases we find the parts
of one whorl opposite or superposed to those of the next whorl.
In some cases, as in the vine-family Ampelidaceae, this seems
to be the ordinary mode of development, but the superposition
of the stamens on the sepals in many plants, as in the pink family,
Caryophyllaceae, is due to the suppression or abortion of the
whorl of petals, and this idea is borne out by the development,
in some plants of the order, of the suppressed whorl. As a rule,
whenever we find the parts of one whorl superposed on those of
another we may suspect some abnormality.

Fig. 33.—Diagrammatic section
of a symmetrical pentamerous
flower of Stone-crop (Sedum), consisting
of five sepals (s), five petals
(p) alternating with the sepals, ten
stamens (a) in two rows, and five
carpels (c) containing ovules. The
dark lines (d) on the outside of the
carpels are glands.

Fig. 34.—Diagram of the flower
of Flax (Linum), consisting of five
sepals (s), five petals (p), five
stamens (a), and five carpels (c),
each of which is partially divided
into two. The dots represent a
whorl of stamens which has disappeared.
It is pentamerous, complete,
symmetrical and regular.

Fig. 35.—Diagram of the flower
of Heath (Erica), a regular tetramerous
flower.

Fig. 36.—Diagram of the trimerous
symmetrical flower of Iris.

Fig. 37.—Diagram of the symmetrical
trimerous flower of Fritillary
(Fritillaria).

Fig. 38.—Diagram of the flower
of Saxifrage (Saxifraga tridactylites).
The calyx and corolla consist of
five parts, the stamens are ten in
two rows, while the pistil has only
two parts developed.

A flower is said to be symmetrical when each of its whorls
consists of an equal number of parts, or when the parts of any
one whorl are multiples of that preceding it. Thus, a symmetrical
flower may have five sepals, five petals, five stamens and
five carpels, or the number of any of these parts may be ten,
twenty or some multiple of five. Fig. 23 is a diagram of a
symmetrical flower, with five parts in each whorl, alternating
with each other. Fig. 33 is a diagram of a symmetrical flower
of stone-crop, with five sepals, five alternating petals, ten
stamens and five carpels. Here the number of parts in the
staminal whorl is double that in the others, and in such a case
the additional five parts form a second row alternating with
the others. In the staminal whorl especially it is common to
find additional rows. Fig. 34 shows a symmetrical flower, with
five parts in the three outer rows, and ten divisions in the inner.
In this case it is the gynoecium which has an additional number
of parts. Fig. 35 shows a flower of heath, with four divisions
of the calyx and corolla, eight stamens in two rows, and four
divisions of the pistil. In fig.
36 there are three parts in
each whorl; and in fig. 37
there are three divisions of
the calyx, corolla and pistil,
and six stamens in two rows.
In all these cases the flower
is symmetrical. In Monocotyledons
it is usual for the
staminal whorl to be double,
it rarely having more than
two rows, whilst amongst
dicotyledons there are often
very numerous rows of
stamens. The floral envelopes
are rarely multiplied. Flowers
in which the number of parts
in each whorl is the same, are
isomerous (of equal number);
when the number in some of
the whorls is different, the
flower is anisomerous (of unequal
number). The pistillate
whorl is very liable to
changes. It frequently
happens that when it is fully
formed, the number of its
parts is not in conformity
with that of the other whorls.
In such circumstances, however,
a flower has been called
symmetrical, provided the
parts of the other whorls are
normal,—the permanent state
of the pistil not being taken
into account in determining
symmetry. Thus fig. 38 shows
a pentamerous symmetrical
flower, with dimerous pistil.
Symmetry, then, in botanical
language, has reference to a
certain definite numerical
relation of parts. A flower
in which the parts are
arranged in twos is called
dimerous; when the parts of
the whorls are three, four or
five, the flower is trimerous,
tetramerous or pentamerous,
respectively. The symmetry
which is most commonly met with is trimerous and pentamerous—the
former occurring generally among monocotyledons, the
latter among dicotyledons. Dimerous and tetramerous symmetry
occur also among dicotyledons.

The various parts of the flower have a certain definite relation
to the axis. Thus, in axillary tetramerous flowers (fig. 35), one
sepal is next the axis, and is called superior or posterior; another
is next the bract, and is inferior or anterior, and the other two
are lateral; and certain terms are used to indicate that position.
A plane passing through the anterior and posterior sepal and
through the floral axis is termed the median plane of the flower;
a plane cutting it at right angles, and passing through the lateral
sepals, is the lateral plane; whilst the planes which bisect the ​angles formed by the lateral and median planes are the diagonalplanes, and in these flowers the petals which alternate with the
sepals are cut by the diagonal planes.

In a pentamerous flower one sepal may be superior, as in the
calyx of Rosaceae and Labiatae; or it may be inferior, as in
the calyx of Leguminosae (fig. 39)—the reverse, by the law of
alternation, being the case with the petals. Thus, in the blossom
of the pea (figs. 39, 40), the odd petal (vexillum) st is superior,
while the odd sepal is inferior. In the order Scrophulariaceae
one of the two carpels is posterior and the other anterior, whilst
in Convolvulaceae the carpels are arranged laterally. Sometimes
the twisting of a part makes a change in the position of other
parts, as in Orchids, where the twisting of the ovary changes
the position of the labellum.

Fig. 39.—Diagram of flower
of Sweet-pea (Lathyrus), showing
five sepals (s), two superior, one
inferior, and two lateral; five
petals (p), one superior, two inferior,
and two lateral; ten
stamens in two rows (a); and
one carpel (c).

Fig. 40.—Flower of Pea
(Pisum sativum), showing a papilionaceous
corolla, with one
petal superior (st) called the
standard (vexillum), two inferior
(car) called the keel (carina),
and two lateral (a) called wings
(alae). The calyx is marked c.

When the different members of each whorl are like in size and
shape, the flower is said to be regular; while differences in the
size and shape of the parts of a whorl make the flower irregular,
as in the papilionaceous flower, represented in fig. 39. When a
flower can be divided by a single plane into two exactly similar
parts; then it is said to be zygomorphic. Such flowers as Papilionaceae,
Labiatae, are examples. In contrast with this are
polysymmetrical or actinomorphic flowers, which have a radial
symmetry and can be divided by several planes into several
exactly similar portions; such are all regular, symmetrical
flowers. When the parts of any whorl are not equal to or some
multiple of the others, then the flower is asymmetrical. This
want of symmetry may be brought about in various ways.
Alteration in the symmetrical arrangement as well as in the
completeness and regularity of flowers has been traced to suppression
or the non-development of parts, degeneration or imperfect
formation, cohesion or union of parts of the same whorl, adhesion
or union of the parts of different whorls, multiplication of parts,
and deduplication (sometimes called chorisis) or splitting of parts.

By suppression or non-appearance of a part at the place where
it ought to appear if the structure was normal, the symmetry
or completeness of the flower is disturbed. This suppression
when confined to the parts of certain verticils makes the flower
asymmetrical. Thus, in many Caryophyllaceae, as Polycarpon
and Holosteum, while the calyx and corolla are pentamerous,
there are only three or four stamens and three carpels; in
Impatiens Noli-me-tangere the calyx is composed of three parts,
while the other verticils have five; in labiate flowers there are
five parts of the calyx and corolla, and only four stamens; and
in Tropaeolum pentaphyllum there are five sepals, two petals,
eight stamens and three carpels. In all these cases the want of
symmetry is traced to the suppression of certain parts. In the
last-mentioned plant the normal number is five, hence it is said
that there are three petals suppressed, as shown by the position
of the two remaining ones; there are two rows of stamens,
in each of which one is wanting; and there are two carpels
suppressed. In many instances the parts which are afterwards
suppressed can be seen in the early stages of growth, and occasionally
some vestiges of them remain in the fully developed flower.
By the suppression of the verticil of the stamens, or of the
carpels, flowers become unisexual or diclinous, and by the
suppression of one or both of the floral envelopes, monochlamydeous
and achlamydeous flowers are produced. The suppression
of parts of the flower may be carried so far that at last a flower
consists of only one part of one whorl. In the Euphorbiaceae we
have an excellent example of the gradual suppression of parts,
where from an apetalous, trimerous, staminal flower we pass to
one where one of the stamens is suppressed, and then to forms
where two of them are wanting. We next have flowers in which
the calyx is suppressed, and its place occupied by one, two or
three bracts (so that the flower is, properly speaking, achlamydeous),
and only one or two stamens are produced. And finally,
we find flowers consisting of a single stamen with a bract. There
is thus traced a degradation, as it is called, from a flower with
three stamens and three divisions of the calyx, to one with a
single bract and a single stamen.

Degeneration, or the transformation of parts, often gives rise
either to an apparent want of symmetry or to irregularity in
form. In unisexual flowers it is not uncommon to find vestiges
of the undeveloped stamens in the form of filiform bodies or
scales. In double flowers transformations of the stamens and
pistils take place, so that they appear as petals. In Canna,
what are called petals are in reality metamorphosed stamens.
In the capitula of Compositae we sometimes find the florets
converted into green leaves. The limb of the calyx may appear
as a rim, as in some Umbelliferae; or as pappus, in Compositae
and Valeriana. In Scrophularia the fifth stamen appears as a
scale-like body; in other Scrophulariaceae, as in Pentstemon,
it assumes the form of a filament, with hairs at its apex in place
of an anther.

Cohesion, or the union of parts of the same whorl, and adhesion,
or the growing together of parts of different whorls, are causes
of change both as regards form and symmetry. Thus in Cucurbita
the stamens are originally five in number, but subsequently
some cohere, so that three stamens only are seen in the mature
flower. Adhesion is well seen in the gynostemium of orchids,
where the stamens and stigmas adhere. In Capparidaceae
the calyx and petals occupy their usual position, but the axis
is prolonged in the form of a gynophore, to which the stamens
are united.

Multiplication, or an increase of the number of parts, gives
rise to changes. We have already alluded to the interposition
of new members in a whorl. This takes place chiefly in the
staminal whorl, but usually the additional parts produced form
a symmetrical whorl with the others. In some instances,
however, this is not the case. Thus in the horse-chestnut there
is an interposition of two stamens, and thus seven stamens are
formed in the flower, which is asymmetrical.

Parts of the flower are often increased by a process of deduplication,
or chorisis, i.e. the splitting of a part so that two or more
parts are formed out of what was originally one. Thus in Cruciferous
plants the staminal whorl consists of four long stamens
and two short ones (tetradynamous). The symmetry in the flower
is evidently dimerous, and the abnormality in the androecium,
where the four long stamens are opposite the posterior sepals,
takes place by a splitting, at a very early stage of development,
of a single outgrowth into two. Many cases of what was considered
chorisis are in reality due to the development of stipules
from the staminal leaf. Thus in Dicentra and Corydalis there
are six stamens in two bundles; the central one of each bundle
alone is perfect, the lateral ones have each only half an anther,
and are really stipules formed from the staminal leaf. Branching
of stamens also produces apparent want of symmetry; thus,
in the so-called polyadelphous stamens of Hypericaceae there
are really only five stamens which give off numerous branches,
but the basal portion remaining short, the branches have the
appearance of separate stamens, and the flower thus seems
asymmetrical.

Cultivation has a great effect in causing changes in the various
parts of plants. Many alterations in form, size, number and
adhesion of parts are due to the art of the horticulturist. The
changes in the colour and forms of flowers thus produced are
endless. In the dahlia the florets are rendered quilled, and are
made to assume many glowing colours. In pelargonium the
flowers have been rendered larger and more showy; and such is ​also the case with the Ranunculus, the auricula and the carnation.
Some flowers, with spurred petals in their usual state,
as columbine, are changed so that the spurs disappear; and
others, as Linaria, in which one petal only is usually spurred,
are altered so as to have all the petals spurred, and to present
what are called pelorian varieties.

Fig. 42.—Diagram to illustrate valvular or valvate aestivation, in
which the parts are placed in a circle, without overlapping or folding.

Fig. 43.—Diagram to illustrate induplicative or induplicate
aestivation, in which the parts of the verticil are slightly turned
inwards at the edges.

As a convenient method of expressing the arrangement of the
parts of the flower, floral formulae have been devised. Several
modes of expression are employed. The following is a very
simple mode which has been proposed:—The several whorls
are represented by the letters S (sepals), P (petals), St (stamens),
C (carpels), and a figure marked after each indicates the number
of parts in that whorl. Thus the formula S5P5St5C5 means that
the flower is perfect, and has pentamerous symmetry, the whorls
being isomerous. Such a flower as that of Sedum (fig. 33) would
be represented by the formula S5P5St5+5C5, where St5+5 indicates
that the staminal whorl consists of two rows of five parts each.
A flower such as the male flower of the nettle (fig. 41) would be
expressed S4P0St4C0. When no other mark is appended the
whorls are supposed to be alternate; but if it is desired to mark
the position of the whorls special symbols are employed. Thus,
to express the superposition of one whorl upon another, a line is
drawn between them, e.g. the symbol S5P5 | St5C5 is the formula
of the flower of Primulaceae.

Fig. 44.

Fig. 45.

Fig. 46.

Fig. 44.—Diagram to illustrate reduplicative or reduplicate
aestivation, in which the parts of the whorl are slightly turned outwards
at the edges.

Fig. 45.—Diagram to illustrate contorted or twisted aestivation, in
which the parts of the whorl are overlapped by each other in turn,
and are twisted on their axis.

Fig. 46.—Diagram to illustrate the quincuncial aestivation, in
which the parts of the flower are arranged in a spiral cycle, so that
1 and 2 are wholly external, 4 and 5 are internal, and 3 is partly
external and partly overlapped by 1.

Fig. 47.

Fig. 48.

Fig. 47.—Diagram to illustrate imbricated
aestivation, in which the
parts are arranged in a spiral cycle,
following the order indicated by the
figures 1, 2, 3, 4, 5.

4, The vexillum or standard, which,
in place of being internal, as
marked by the dotted line, becomes
external.

5, The remaining part of the keel.

The order of the cycle is indicated
by the figures.

The manner in which the parts are arranged in the flower-bud
with respect to each other before opening is the aestivation or
praefloration. The latter terms are applied to the flower-bud
in the same way as vernation is to the leaf-bud, and distinctive
names have been given to the different arrangements exhibited,
both by the leaves individually and in their relations to each
other. As regards each leaf of the flower, it is either spread out,
as the sepals in the bud of the lime-tree, or folded upon itself
(conduplicate), as in the petals of some species of Lysimachia,
or slightly folded inwards or outwards at the edges, as in the
calyx of some species of clematis and of some herbaceous plants,
or rolled up at the edges (involute or revolute), or folded transversely,
becoming crumpled or corrugated, as in the poppy.
When the parts of a whorl are placed in an exact circle, and are
applied to each other by their edges only, without overlapping
or being folded, thus resembling the valves of a seed-vessel,
the aestivation is valvate (fig. 42). The edges of each of the parts
may be turned either inwards or outwards; in the former case
the aestivation is induplicate (fig. 43), in the latter case reduplicate
(fig. 44). When the parts of a single whorl are placed in a circle,
each of them exhibiting a torsion of its axis, so that by one of its
sides it overlaps its neighbour, whilst its side is overlapped in like
manner by that standing next to it, the aestivation is twisted
or contorted (fig. 45). This arrangement is characteristic of the
flower-buds of Malvaceae and Apocynaceae, and it is also seen
in Convolvulaceae and Caryophyllaceae. When the flower
expands, the traces of twisting often disappear, but sometimes,
as in Apocynaceae, they remain. Those forms of aestivation
are such as occur in cyclic flowers, and they are included under
circular aestivation. But in spiral flowers we have a different
arrangement; thus the leaves of the calyx of Camellia japonica
cover each other partially like tiles on a house. This aestivation
is imbricate. At other times, as in the petals of Camellia, the
parts envelop each other completely, so as to become convolute.
This is also seen in a transverse section of the calyx of Magnoliagrandiflora, where each of the three leaves embraces that within
it. When the parts of a whorl are five, as occurs in many
dicotyledons, and the imbrication is such that there are two
parts external, two internal, and a fifth which partially covers
one of the internal parts by
its margin, and is in its
turn partially covered by
one of the external parts,
the aestivation is quincuncial
(fig. 46). This quincunx
is common in the
corolla of Rosaceae. In
fig. 47 a section is given
of the bud of Antirrhinummajus, showing the imbricate
spiral arrangement.
In this case it will be seen
that the part marked 5 has,
by a slight change in position,
become overlapped by
1. This variety of imbricate
aestivation has been
termed cochlear. In flowers
such as those of the pea
(fig. 40), one of the parts,
the vexillum, is often large
and folded over the others,
giving rise to vexillary
aestivation (fig. 48), or the
carina may perform a similar office, and then the aestivation is
carinal, as in the Judas-tree (Cercis Siliquastrum). The parts of
the several verticils often differ in their mode of aestivation.
Thus, in Malvaceae the corolla is contorted and the calyx valvate,
or reduplicate; in St John’s-wort the calyx is imbricate, and
the corolla contorted. In Convolvulaceae, while the corolla is
twisted, and has its parts arranged in a circle, the calyx is imbricate,
and exhibits a spiral arrangement. In Guazuma the calyx
is valvate, and the corolla induplicate. The circular aestivation
is generally associated with a regular calyx and corolla, while the
spiral aestivations are connected with irregular as well as with
regular forms.

The sepals are sometimes free or separate from each other,
at other times they are united to a greater or less extent; in the
former case, the calyx is polysepalous, in the latter
gamosepalous or monosepalous. The divisions of the
Calyx.
calyx present usually the characters of leaves, and in some cases
of monstrosity they are converted into leaf-like organs, as not
infrequently happens in primulas. They are usually entire,
but occasionally they are cut in various ways, as in the rose;
they are rarely stalked. Sepals are generally of a more or less
oval, elliptical or oblong form, with their apices either blunt or ​acute. In their direction they are erect or reflexed (with their
apices downwards), spreading outwards (divergent or patulous),
or arched inwards (connivent). They are usually of a greenish
colour (herbaceous); but sometimes they are coloured or
petaloid, as in the fuchsia, tropāeolum, globe-flower and
pomegranate. Whatever be its colour, the external envelope
of the flower is considered as the calyx. The vascular bundles
sometimes form a prominent rib, which indicates the middle of
the sepal; at other times they form several ribs. The venation
is useful as pointing out the number of leaves which constitute
a gamosepalous calyx. In a polysepalous calyx the number
of the parts is indicated by Greek numerals prefixed; thus,
a calyx which has three sepals is trisepalous; one with five sepals
is pentasepalous. The sepals occasionally are of different forms
and sizes. In Aconite one of them is shaped like a helmet
(galeate). In a gamosepalous calyx the sepals are united in
various ways, sometimes very slightly, and their number is
marked by the divisions at the apex. These divisions either
are simple projections in the form of acute or obtuse teeth
(fig. 49); or they extend down the calyx as fissures about half-way,
the calyx being trifid (three-cleft), quinquefid (five-cleft), &c.,
according to their number; or they reach to near the base in the
form of partitions, the calyx being tripartite, quadripartite,
quinquepartite, &c. The union of the parts may be complete,
and the calyx may be quite entire or truncate, as in some Correas,
the venation being the chief indication of the different parts.
The cohesion is sometimes irregular, some parts uniting to a
greater extent than others; thus a two-lipped or labiate calyx
is formed. The upper lip is often composed of three parts,
which are thus posterior or next the axis, while the lower has
two, which are anterior. The part formed by the union of the
sepals is called the tube of the calyx; the portion where the sepals
are free is the limb.

From Strasburger’s Lehrbuch der
Botanik, by permission of Gustav
Fischer.

Fig. 49.

Fig. 50.

Fig. 51.

Fig. 52.

Fig. 53.

Fig. 49.—Gamosepalous five-toothed calyx of Campion (Lychnis).

Fig. 50.—Obsolete calyx (c) of Madder (Rubia) adherent to the
pistil, in the form of a rim.

Occasionally, certain parts of the sepals undergo marked
enlargement. In the violet the calycine segments are prolonged
downwards beyond their insertions, and in the Indian cress
(Tropaeolum) this prolongation is in the form of a spur (calcar),
formed by three sepals; in Delphinium it is formed by one.
In Pelargonium the spur from one of the sepals is adherent to
the flower-stalk. In Potentilla and allied genera an epicalyx is
formed by the development of stipules from the sepals, which
form an apparent outer calyx, the parts of which alternate with
the true sepals. In Malvaceae an epicalyx is formed by the
bracteoles. Degenerations take place in the calyx, so that it
becomes dry, scaly and glumaceous (like the glumes of grasses),
as in the rushes (Juncaceae); hairy, as in Compositae; or a
mere rim, as in some Umbelliferae and Acanthaceae, and in
Madder (Rubia tinctorum, fig. 50), when it is called obsolete or
marginate. In Compositae, Dipsacaceae and Valerianaceae
the calyx is attached to the pistil, and its limb is developed in
the form of hairs called pappus (fig. 51). This pappus is either
simple (pilose) or feathery (plumose). In Valeriana the superior
calyx is at first an obsolete rim, but as the fruit ripens it is shown
to consist of hairs rolled inwards, which expand so as to waft
the fruit. The calyx sometimes falls off before the flower
expands, as in poppies, and is caducous (fig. 52); or along with
the corolla, as in Ranunculus, and is deciduous; or it remains
after flowering (persistent) as in Labiatae, Scrophulariaceae,
and Boraginaceae; or its base only is persistent, as in DaturaStramonium. In Eschscholtzia and Eucalyptus the sepals remain
united at the upper part, and become disarticulated at the base
or middle, so as to come off in the form of a lid or funnel. Such
a calyx is operculate or calyptrate. The existence or non-existence
of an articulation determines the deciduous or persistent nature
of the calyx.

The receptacle bearing the calyx is sometimes united to the
pistil, and enlarges so as to form a part of the fruit, as in the
apple, pear, &c. In these fruits the withered calyx is seen at
the apex. Sometimes a persistent calyx increases much after
flowering, and encloses the fruit without being incorporated
with it, becoming accrescent, as in various species of Physalis
(fig. 53); at other times it remains in a withered or marcescent
form, as in Erica; sometimes it becomes inflated or vesicular,
as in sea campion (Silene maritima).

The corolla is the more or less coloured attractive inner floral
envelope; generally the most conspicuous whorl. It is present
in the greater number of Dicotyledons. Petals differ
more from ordinary leaves than sepals do, and are
Corolla.
much more nearly allied to the staminal whorl. In some cases,
however, they are transformed into leaves, like the calyx, and
occasionally leaf-buds are developed in their axil They are
seldom green, although occasionally that colour is met with, as
in some species of Cobaea, Hoya viridiflora, Gonolobus viridiflorus
and Pentatropis spiralis. As a rule they are highly coloured,
the colouring matter being contained in the cell-sap, as in blue
or red flowers, or in plastids (chromoplasts), as generally in yellow
flowers, or in both forms, as in many orange-coloured or reddish
flowers. The attractiveness of the petal is often due wholly or
in part to surface markings; thus the cuticle of the petal of a
pelargonium, when viewed with a ½ or ¼-in. object-glass, shows
beautiful hexagons, the boundaries of which are ornamented with
several inflected loops in the sides of the cells.

Petals are generally glabrous or smooth; but, in some
instances, hairs are produced on their surface. Petaline hairs,
though sparse and scattered, present occasionally the same
arrangement as those which occur on the leaves; thus, in
Bombaceae they are stellate. Coloured hairs are seen on the
petals of Menyanthes, and on the segments of the perianth of
Iris. They serve various purposes in the economy of the flower,
often closing the way to the honey-secreting part of the flower
to small insects, whose visits would be useless for purposes of
pollination. Although petals are usually very thin and delicate
in their texture, they occasionally become thick and fleshy,
as in Stapelia and Rafflesia; or dry, as in heaths; or hard and
stiff, as in Xylopia. A petal often consists of two portions—the
lower narrow, resembling the petiole of a leaf, and called the
unguis or claw; the upper broader, like the blade of a leaf, and
called the lamina or limb. These parts are seen in the petals
of the wallflower (fig. 54). The claw is often wanting, as in the
crowfoot (fig. 55) and the poppy, and the petals are then sessile.
According to the development of veins and the growth of cellular
tissue, petals present varieties similar to those of leaves. Thus
the margin is either entire or divided into lobes or teeth. These
teeth sometimes form a regular fringe round the margin, and the ​petal becomes fimbriated, as in the pink; or laciniated, as in
Lychnis Flos-cuculi; or crested, as in Polygala. Sometimes the
petal becomes pinnatifid, as in Schizopetalum. The median vein
is occasionally prolonged beyond the summit of the petals in
the form of a long process, as in Strophanthus hispidus, where
it extends for 7 in.; or the prolonged extremity is folded downwards
or inflexed, as in Umbelliferae, so that the apex approaches
the base. The limb of the petal may be flat or concave, or
hollowed like a boat. In Hellebore the petals become folded
in a tubular form, resembling a horn (fig. 56); in aconite (fig. 58)
some of the petals resemble a hollow-curved horn, supported
on a grooved stalk; while in columbine, violet (fig. 57),
snapdragon and Centranthus, one or all of them are prolonged
in the form of a spur, and are calcarate. In Valeriana, Antirrhinum
and Corydalis, the spur is very short, and the corolla
or petal is said to be gibbous, or saccate, at the base. These spurs,
tubes and sacs serve as receptacles for the secretion or containing
of nectar.

Fig. 54.

Fig. 55.

Fig. 56.

Fig. 57.

Fig. 58.

Fig. 54.—Unguiculate or clawed petal of Wallflower (CheiranthusCheiri). c, The claw or unguis; l, the blade or lamina.

Fig. 55.—Petal of Crowfoot (Ranunculus), without a claw, and
thus resembling a sessile leaf. At the base of the petal a nectariferous
scale is seen.

Fig. 58.—Part of the flower of Aconite (Aconitum Napellus), showing
two irregular horn-like petals (p) supported on grooved stalks (o).
These serve as nectaries, s, the whorl of stamens inserted on the
thalamus and surrounding the pistil.

A corolla is dipetalous, tripetalous, tetrapetalous or pentapetalous
according as it has two, three, four or five separate petals. The
general name of polypetalous is given to corollas having separate
petals, while monopetalous, gamopetalous or sympetalous is applied
to those in which the petals are united. This union generally
takes place at the base, and extends more or less towards the
apex; in Phyteuma the petals are united at their apices also.
In some polypetalous corollas, as that of the vine, the petals are
separate at the base and adhere by the apices. When the petals
are equal as regards their development and size, the corolla is
regular; when unequal, it is irregular. When a corolla is gamopetalous
it usually happens that the lower portion forms a
tube, while the upper parts are either free or partially united,
so as to form a common limb, the point of union of the two
portions being the throat, which often exhibits a distinct constriction
or dilatation. The number of parts forming such a corolla
can be determined by the divisions, whether existing as teeth,
crenations, fissures or partitions, or if, as rarely happens, the
corolla is entire, by the venation. The union may be equal
among the parts, or some may unite more than others.

Fig. 59.—Rosaceous
corolla (c) of the Strawberry
(Fragaria vesca),
composed of five petals
without claws.

Amongst regular polypetalous corollas may be noticed the
rosaceous corolla (fig. 59), in which there are five spreading
petals, having no claws, and arranged as in the rose, strawberry
and Potentilla; the caryophyllaceous corolla, in which there are
five petals with long, narrow, tapering claws, as in many of the
pink tribe; the cruciform, having four
petals, often unguiculate, placed opposite
in the form of a cross, as seen in wallflower,
and in other plants called cruciferous.
Of irregular polypetalous corollas
the most marked is the papilionaceous
(fig. 40), in which there are five petals:—one
superior (posterior), st, placed
next to the axis, usually larger than the
rest, called the vexillum or standard;
two lateral, a, the alae or wings; two
inferior (anterior), partially or completely
covered by the alae, and often united slightly by their
lower margins, so as to form a single keel-like piece, car, called
carina, or keel, which embraces the essential organs. This form
of corolla is characteristic of British leguminous plants.

From Strasburger’s Lehrbuch der Botanik, by permission
of Gustav Fischer.

Fig. 60.—Flower of Campanula medium;d, bract; v, bracteoles.

Regular gamopetalous corollas are sometimes campanulate or
bell-shaped, as in (Campanula) (fig. 60); infundibuliform or
funnel-shaped, when the tube is like an inverted cone, and the
limb becomes more expanded at the apex, as in tobacco; hypocrateriform
or salver-shaped, when there is a straight tube surmounted
by a flat spreading limb, as in primula (fig. 61); tubular,
having a long cylindrical tube, appearing continuous with the
limb, as in Spigelia and comfrey; rotate or wheel-shaped, when
the tube is very short, and the limb flat and spreading, as in
forget-me-not, Myosotis (when the divisions of the rotate corolla
are very acute, as in Galium, it is sometimes called stellate or
star-like); urceolate or urn-shaped, when there is scarcely any
limb, and the tube is narrow at both ends, and expanded in the
middle, as in bell-heath (Erica cinerea). Some of these forms
may become irregular in consequence of certain parts being more
developed than others. Thus, in Veronica, the rotate corolla
has one division much smaller than the rest, and in foxglove
(Digitalis) there is a
slightly irregular
companulate corolla.
Of irregular
gamopetalous corollas
there may be
mentioned the labiate
or lipped (fig. 62),
having two divisions
of the limb in the
form of lips (the
upper one, u, composed
usually of two
united petals, and
the lower, l, of three),
separated by a gap.
In such cases the tube varies in length, and the parts in their
union follow the reverse order of what occurs in the calyx, where
two sepals are united in the lower lip and three in the upper.
When the upper lip of a labiate corolla is much arched, and the
lips separated by a distinct gap, it is called ringent (fig. 62). The
labiate corolla characterizes the natural order Labiatae. When
the lower lip is pressed against the upper, so as to leave only a
chink between them, the corolla is said to be personate, as in
snapdragon, and some other Scrophulariaceae. In some corollas
the two lips become hollowed out in a remarkable manner, as in
calceolaria, assuming a slipper-like appearance, similar to what
occurs in the labellum of some orchids, as Cypripedium. When a
tubular corolla is split in such a way as to form a strap-like process
on one side with several tooth-like projections at its apex, it
becomes ligulate or strap-shaped (fig. 63). This corolla occurs
in many composite plants, as in the florets of dandelion, daisy
and chicory. The number of divisions at the apex indicates the
number of united petals, some of which, however, may be ​abortive. Occasionally some of the petals become more united
than others, and then the corolla assumes a bilabiate or two-lipped
form, as seen in the division of Compositae called Labiatiflorae.

Petals are sometimes suppressed, and sometimes the whole
corolla is absent. In Amorpha and Afzelia the corolla is reduced to
a single petal, and in some other Leguminous plants it is entirely
wanting. In the natural order Ranunculaceae, some genera, such
as Ranunculus, globe-flower and paeony, have both calyx and
corolla, while others, such as clematis, anemone and Caltha, have
only a coloured calyx. Flowers become double by the multiplication
of the parts of the corolline whorl; this arises in general
from a metamorphosis of the stamens.

Fig. 61.

Fig. 62.

Fig. 63.

Fig. 61.—Flower of cowslip (Primulaveris) cut vertically. s, Sepals
joined to form a gamosepalous calyx;
c, corolla consisting of tube and spreading
limb; a, stamens springing from
the mouth of the tube; p, pistil.

Fig. 62.—Irregular gamopetalous
labiate corolla of the Dead-nettle
(Lamium album). The upper lip u is
composed of two petals united, the
lower lip (l) of three. Between the
two lips there is a gap. The throat is
the part where the tube and the labiate
limb join. From the arching of the
upper lip this corolla is called ringent.

Fig. 63.—Irregular gamopetalous
ligulate flower of Ragwort (Senecio).
It is a tubular floret, split down on one
side, with the united petals forming a
straplike projection. The lines on the
flat portion indicate the divisions of the
five petals. From the tubular portion
below, the bifid style projects slightly.

Certain structures occur on the petals of some flowers, which
received in former days the name of nectaries. The term nectary
was very vaguely applied
by Linnaeus to any part
of the flower which presented
an unusual aspect,
as the crown (corona) of
narcissus, the fringes of
the Passion-flower, &c. If
the name is retained it
ought properly to include
only those parts which
secrete a honey-like substance,
as the glandular
depression at the base of
the perianth of the fritillary,
or on the petal of
Ranunculus (fig. 55), or on
the stamens of Rutaceae.
The honey secreted by
flowers attracts insects,
which, by conveying the
pollen to the stigma,
effect fertilization. The
horn-like nectaries under
the galeate sepal of
aconite (fig. 58) are modified
petals, so also are the
tubular nectaries of hellebore
(fig. 56). Other
modifications of some part
of the flower, especially
of the corolla and stamens,
are produced either by
degeneration or outgrowth,
or by chorisis,
or deduplication. Of this nature are the scales on the petals in
Lychnis, Silene and Cynoglossum, which are formed in the same
way as the ligules of grasses. In other cases, as in Samolus,
the scales are alternate with the petals, and may represent altered
stamens. In Narcissus the appendages are united to form a
crown, consisting of a membrane similar to that which unites
the stamens in Pancratium. It is sometimes difficult to say
whether these structures are to be referred to the corolline or to
the staminal row.

Petals are attached to the axis usually by a narrow base.
When this attachment takes place by an articulation, the petals
fall off either immediately after expansion (caducous) or after
fertilization (deciduous). A corolla which is continuous with the
axis and not articulated to it, as in campanula and heaths,
may be persistent, and remain in a withered or marcescent state
while the fruit is ripening. A gamopetalous corolla falls off in
one piece; but sometimes the base of the corolla remains persistent,
as in Rhinanthus and Orobanche.

The stamens and the pistil are sometimes spoken of as the
essential organs of the flower, as the presence of both is required
in order that perfect seed may be produced. As with few exceptions
the stamen represents a leaf which has been specially
developed to bear the pollen or microspores, it is spoken of in
comparative morphology as a microsporophyll; similarly the
carpels which make up the pistil are the megasporophylls (see
Angiosperms). Hermaphrodite or bisexual flowers are those
in which both these organs are found; unisexual or diclinous
are those in which only one of these organs appears,—those
bearing stamens only, being staminiferous or “male”; those
having the pistil only, pistilliferous or “female.” But even in
plants with hermaphrodite flowers self-fertilization is often provided
against by the structure of the parts or by the period of
ripening of the organs. For instance, in Primula and Linum
some flowers have long stamens and a pistil with a short style,
the others having short stamens and a pistil with a long style.
The former occur in the so-called thrum-eyed primroses (fig. 61),
the latter in the “pin-eyed.” Such plants are called dimorphic.
Other plants are trimorphic, as species of Lythrum, and proper
fertilization is only effected by combination of parts of equal
length. In some plants the stamens are perfected before the
pistil; these are called proterandrous, as in Ranunculus repens,
Silene maritima, Zea Mays. In other plants, but more rarely,
the pistil is perfected before the stamens, as in Potentilla argentea,
Plantago major, Coix Lachryma, and they are termed proterogynous.
Plants in which proterandry or proterogyny occurs
are called dichogamous. When in the same plant there are
unisexual flowers, both male and female, the plant is said to be
monoecious, as in the hazel and castor-oil plant. When the male
and female flowers of a species are found on separate plants,
the term dioecious is applied, as in Mercurialis and hemp; and
when a species has male, female and hermaphrodite flowers
on the same or different plants, as in Parietaria, it is polygamous.

From Strasburger’s Lehrbuch der Botanik, by permission
of Gustav Fischer.

The stamens arise from the thalamus or torus within the
petals, with which they generally alternate, forming one or more
whorls, which collectively constitute the androecium.
Their normal position is below the pistil, and when
Stamens.
they are so placed (fig. 64, a) upon the thalamus they are hypogynous.
Sometimes they become adherent to the petals, or are
epipetalous, and the insertion of both is looked upon as similar,
so that they are still hypogynous, provided they are independent
of the calyx and the pistil. In other cases they are perigynous
or epigynous (fig. 65). Numerous intermediate forms occur,
especially amongst Saxifragaceae, where the parts are half superior
or half inferior. Where the stamens become adherent to the
pistil so as to form a column, the flowers are said to be gynandrous,
as in Aristolochia (fig.
66). These arrangements
of parts are of
great importance in
classification. The
stamens vary in number
from one to many
hundreds. In acyclic
flowers there is often
a gradual transition
from petals to
stamens, as in the
white water-lily (fig.
31). When flowers become
double by cultivation,
the stamens
are converted into
petals, as in the
paeony, camellia,
rose, &c. When there is only one whorl the stamens are
usually equal in number to the sepals or petals, and are
arranged opposite to the former, and alternate with the latter.
The flower is then isostemonous. When the stamens are not
equal in number to the sepals or petals, the flower is anisostemonous.
When there is more than one whorl of stamens, then the
parts of each successive whorl alternate with those of the whorl
preceding it. The staminal row is more liable to multiplication
of parts than the outer whorls. A flower with a single row of
stamens is haplostemonous. If the stamens are double the sepals
or petals as regards number, the flower is diplostemonous; if
more than double, polystemonous. The additional rows of ​stamens may be developed in the usual centripetal (acropetal)
order, as in Rhamnaceae; or they may be interposed between
the pre-existing ones or be placed outside them, i.e. develop
centrifugally (basipetally), as in geranium and oxalis, when the
flower is said to be obdiplostemonous. When the stamens are
fewer than twenty they are said to be definite; when above
twenty they are indefinite, and are represented by the symbol ∞.
The number of stamens is indicated by the Greek numerals
prefixed to the term androus; thus a flower with one stamen
is monandrous, with two, three, four, five, six or many stamens,
di-, tri-, tetr-, pent-, hex- or polyandrous, respectively.

From Strasburger’s Lehrbuch der Botanik, by permission
of Gustav Fischer.

Fig. 66.—Flowers of Aristolochia Clematitis
cut through longitudinally. I. Young
flower in which the stigma (N) is receptive
and the stamens (S) have not yet opened;
II. Older flower with the stamens (S)
opened, the stigma withered, and the hairs
on the corolla dried up.

Fig. 65.—Flower of
Aralia in vertical section.
c, Calyx; p, petal;
e, stamen; s, stigmas.
The calyx, petals and
stamens spring from
above the ovary (o) in
which two chambers
are shown each with a
pendulous ovule; d, disc
between the stamens
and stigmas.

The function of the stamen is the development and distribution
of the pollen. The stamen usually consists of two parts, a contracted
portion, often thread-like, termed the filament (fig. 25 f),
and a broader portion, usually of two lobes, termed the anther (a),
containing the powdery pollen (p), and supported upon the end
of the filament. That
portion of the filament
in contact with the
anther-lobes is termed
the connective. If the
anther is absent the
stamen is abortive,
and cannot perform
its functions. The
anther is developed
before the filament,
and when the latter is not produced, the anther is sessile, as in
the mistletoe.

The filament is usually, as its name imports, filiform or thread-like,
and cylindrical, or slightly tapering towards its summit.
It is often, however, thickened, compressed and flattened in
various ways, becoming petaloid in Canna, Marania, water-lily
(fig. 32); subulate or slightly broadened at the base and drawn
out into a point like an awl, as in Butomus umbellatus; or
clavate, that is, narrow below and broad above, as in Thalictrum.
In some instances, as in Tamarix gallica, Peganum Harmala,
and Campanula, the base of the filament is much dilated, and
ends suddenly in a narrow thread-like portion. In these cases
the base may give off lateral stipulary processes, as in Allium
and Alyssum calycinum. The filament varies much in length
and in firmness. The length sometimes bears a relation to that
of the pistil, and to the position of the flower, whether erect or
drooping. The filament is usually of sufficient solidity to support
the anther in an erect position; but sometimes, as in grasses,
and other wind-pollinated flowers, it is very delicate and hair-like,
so that the anther is pendulous (fig. 105). The filament is
generally continuous from one end to the other, but in some
cases it is bent or jointed, becoming geniculate; at other times,
as in the pellitory, it is spiral. It is colourless, or of different
colours. Thus in fuchsia and Poinciana, it is red; in Adamia
and Tradescantia virginica, blue; in Oenothera and Ranunculusacris, yellow.

Hairs, scales, teeth or processes of different kinds are
sometimes
times developed on the filament. In spiderwort (Tradescantiavirginica) the hairs are beautifully coloured, moniliform or
necklace-like, and afford good objects for studying rotation
of the protoplasm. Filaments are usually articulated to the
thalamus or torus, and the stamens fall off after fertilization;
but in Campanula and some other plants they are continuous
with the torus, and the stamens remain persistent, although in a
withered state. Changes are produced in the whorl of stamens
by cohesion of the filaments to a greater or less extent, while
the anthers remain free; thus, all the filaments of the androecium
may unite, forming a tube
round the pistil, or a central
bundle when the pistil is abortive,
the stamens becoming
monadelphous, as occurs in
plants of the Mallow tribe; or
they may be arranged in two
bundles, the stamens being
diadelphous, as in Polygala,
Fumaria and Pea; in this case
the bundles may be equal or
unequal. It frequently happens,
especially in Papilionaceous
flowers, that out of ten stamens
nine are united by their filaments,
while one (the posterior
one) is free (fig. 68). When
there are three or more bundles
the stamens are triadelphous, as in Hypericum aegyptiacum, or
polyadelphous, as in Ricinus communis (castor-oil). In some
cases, as in papilionaceous flowers, the stamens cohere, having
been originally separate, but in most cases each bundle is produced
by the branching of a single stamen. When there are
three stamens in a bundle we may conceive the lateral ones
as of a stipulary nature. In Lauraceae there are perfect
stamens, each having at the base of the filament two abortive
stamens or staminodes, which may be analogous to stipules.
Filaments sometimes are adherent to the pistil, forming a column
(gynostemium), as in Stylidium, Asclepiadaceae, Rafflesia, and
Aristolochiaceae (fig. 66); the flowers are then termed gynandrous.

Fig. 68.

Fig. 69.

Fig. 70.

Fig. 68.—Stamens and pistil of Sweet Pea (Lathyrus). The
stamens are diadelphous, nine of them being united by their filaments
(f), while one of them (e) is free; st, stigma; c, calyx.

Fig. 70.—Quadrilocular or tetrathecal anther of the flowering
Rush (Butomus umbellatus). The anther entire (a) with its filament;
section of anther (b) showing the four loculi.

The anther consists of lobes containing the minute powdery
pollen grains, which, when mature, are discharged by a fissure
or opening of some sort. There is a double covering
of the anther—the outer, or exothecium, resembles the
The anther.
epidermis, and often presents stomata and projections of
different kinds (fig. 69); the inner, or endothecium, is formed by a
layer or layers of cellular tissue (fig. 69, cf), the cells of which ​have a spiral, annular, or reticulated thickening of the wall.
The endothecium varies in thickness, generally becoming thinner
towards the part where the anther opens, and there disappears
entirely. The walls of the cells are frequently absorbed, so that
when the anther attains maturity the fibres are alone left, and
these by their elasticity assist in discharging the pollen. The
anther is developed before the filament, and is always sessile in
the first instance, and sometimes continues so. It appears at
first as a simple cellular papilla of meristem, upon which an
indication of two lobes soon appears. Upon these projections
the rudiments of the pollen-sacs are then seen, usually four
in number, two on each lobe. In each a differentiation takes
place in the layers beneath the epidermis, by which an outer layer
of small-celled tissue surrounds an inner portion of large cells.
Those central cells are the mother-cells of the pollen, whilst the
small-celled layer of tissue external to them becomes the endothecium,
the exothecium being formed from the epidermal layer.

In the young state there are usually four pollen-sacs, two for
each anther-lobe, and when these remain permanently complete
it is a quadrilocular or tetrathecal anther (fig. 70). Sometimes,
however, only two cavities remain in the anther, by union of
the sacs in each lobe, in which case the anther is said to be bilocular
or dithecal. Sometimes the anther has a single cavity, and
becomes unilocular, or monothecal, or dimidiate, either by the
disappearance of the partition between the two lobes, or by the
abortion of one of its lobes, as in Styphelia laeta and Althaeaofficinalis (hollyhock). Occasionally there are numerous cavities
in the anther, as in Viscum and Rafflesia. The form of the
anther-lobes varies. They are generally of a more or less oval
or elliptical form, or they may be globular, as in Mercurialisannua; at other times linear or clavate: curved, flexuose, or
sinuose, as in bryony and gourd. According to the amount of
union of the lobes and the unequal development of different
parts of their surface an infinite variety of forms is produced.
That part of the anther to which the filament is attached is the
back, the opposite being the face. The division between the lobes
is marked on the face of the anther by a groove or furrow, and
there is usually on the face a suture, indicating the line of dehiscence.
The suture is often towards one side in consequence of
the valves being unequal. The stamens may cohere by their
anthers, and become syngenesious, as in composite flowers, and in
lobelia, jasione, &c.

The anther-lobes are united to the connective, which is either
continuous with the filament or articulated with it. When the
filament is continuous with the connective, and is
prolonged so that the anther-lobes appear to be united
The connective.
to it throughout their whole length, and lie in apposition
to it and on both sides of it, the anther is said to be adnate or
adherent; when the filament ends at the base of the anther, then
the latter is innate or erect. In these cases the anther is to a
greater or less degree fixed. When, however, the attachment is
very narrow, and an articulation exists, the anthers are movable
(versatile) and are easily turned by the wind, as in Tritonia,
grasses (fig. 105), &c., where the filament is attached only to the
middle of the connective. The connective may unite the anther-lobes
completely or only partially. It is sometimes very short
and is reduced to a mere point, so that the lobes are separate or
free. At other times it is prolonged upwards beyond the lobes,
assuming various forms, as in Acalypha and oleander; or it is
extended backwards and downwards, as in violet (fig. 71),
forming a nectar-secreting spur. In Salvia officinalis the connective
is attached to the filament in a horizontal manner, so as
to separate the two anther-lobes (fig. 72), one only of which
contains pollen, the other being imperfectly developed and sterile.
The connective is joined to the filament by a movable joint
forming a lever which plays an important part in the pollination-mechanism.
In Stachys the connective is expanded laterally,
so as to unite the bases of the anther-lobes and bring them into
a horizontal line.

Fig. 71.

Fig. 73.

Fig. 74.

Fig. 72.

Fig. 75.

Fig. 71.—Two stamens of
Pansy (Viola tricolor), with
their two anther-lobes and the
connectives (p) extending beyond
them. One of the stamens
has been deprived of its spur,
the other shows its spur c.

Fig. 74.—Stamen of a species
of Nightshade (Solanum),
showing the divergence of the
anther-lobes at the base, and
the dehiscence by pores at the
apex.

Fig. 75.—The stamen of the
Barberry (Berberis vulgaris),
showing one of the valves of
the anther (v) curved upwards,
bearing the pollen on its inner
surface.

The opening or dehiscence of the anthers to discharge their
contents takes place either by clefts, by valves, or by pores.
When the anther-lobes are erect, the cleft is lengthwise along the
line of the suture—longitudinal dehiscence (fig. 25). At other
Antherdehiscence.
times the slit is horizontal, from the connective to the
side, as in Alchemilla arvensis (fig. 73) and in Lemna;
the dehiscence is then transverse. When the anther-lobes
are rendered horizontal by the enlargement of the connective,
then what is really longitudinal dehiscence may appear
to be transverse. The cleft does not always proceed the whole
length of the anther-lobe at once,
but often for a time it extends
only partially. In other instances
the opening is confined
to the base or apex, each loculament
opening by a single pore,
as in Pyrola, Tetratheca juncea,
Rhododendron, Vaccinium and
Solanum (fig. 74), where there are
two, and Poranthera, where there
are four; whilst in the mistletoe
the anther has numerous pores
for the discharge of the pollen.
Another mode of dehiscence is
the valvular, as in the barberry
(fig. 75), where each lobe opens
by a valve on the outer side of
the suture, separately rolling up
from base to apex; in some of
the laurel tribe there are two
such valves for each lobe, or four
in all. In some Guttiferae, as
Hebradendron cambogioides (the
Ceylon gamboge plant), the
anther opens by a lid separating
from the apex (circumscissile
dehiscence).

The anthers dehisce at different
periods during the process of
flowering; sometimes in the bud,
but more commonly when the
pistil is fully developed and the
flower is expanded. They either
dehisce simultaneously or in succession.
In the latter case individual
stamens may move in
succession towards the pistil and
discharge their contents, as in
Parnassia palustris, or the outer
or the inner stamens may first
dehisce, following thus a centripetal
or centrifugal order. These
variations are intimately connected
with the arrangements
for transference of pollen. The
anthers are called introrse when
they dehisce by the surface next
to the centre of the flower; they
are extrorse when they dehisce by the outer surface; when they
dehisce by the sides, as in Iris and some grasses, they are
laterally dehiscent. Sometimes, from their versatile nature,
anthers originally introrse become extrorse, as in the Passion-flower
and Oxalis.

The usual colour of anthers is yellow, but they present a great
variety in this respect. They are red in the peach, dark purple in
the poppy and tulip, orange in Eschscholtzia, &c. The colour
and appearance of the anthers often change after they have
discharged their functions.

Stamens occasionally become sterile by the degeneration or
non-development of the anthers, when they are known as
staminodia, or rudimentary stamens. In Scrophularia the fifth
stamen appears in the form of a scale; and in many Pentstemons
it is reduced to a filament with hairs or a shrivelled membrane at
the apex. In other cases, as in double flowers, the stamens are
converted into petals; this is also probably the case with such ​plants as Mesembryanthemum, where there is a multiplication
of petals in several rows. Sometimes, as in Canna, one of the
anther-lobes becomes abortive, and a petaloid appendage is
produced. Stamens vary in length as regards the corolla.
Some are enclosed within the tube of the flower, as in Cinchona
(included); others are exserted, or extend beyond the flower,
as in Littorella or Plantago. Sometimes the stamens in the early
state of the flower project beyond the petals, and in the progress
of growth become included, as in Geranium striatum. Stamens
also vary in their relative lengths. When there is more than one
row or whorl in a flower, those on the outside are sometimes
longest, as in many Rosaceae; at other times those in the interior
are longest, as in Luhea. When the stamens are in two rows,
those opposite the petals are usually shorter than those which
alternate with the petals. It sometimes happens that a single
stamen is longer than
all the rest. A definite
relation, as regards
number, sometimes
exists between the long
and the short stamens.
Thus, in some flowers
the stamens are didynamous,
having only
four out of five stamens
developed, and the
two corresponding to
the upper part of the
flower longer than the
two lateral ones. This
occurs in Labiatae and
Scrophulariaceae (fig.
76). Again, in other
cases there are six
stamens, whereof four
long ones are arranged
in pairs opposite to each
other, and alternate
with two isolated short ones (fig. 77), giving rise to tetradynamous
flowers, as in Cruciferae. Stamens, as regards their direction,
may be erect, turned inwards, outwards, or to one side. In the
last-mentioned case they are called declinate, as in amaryllis,
horse-chestnut and fraxinella.

Fig. 76.—Corolla
of foxglove (Digitalispurpurea), cut
in order to show
the didynamous
stamens (two long
and two short)
which are attached
to it.

From Strasburger’s
Lehrbuch der Botanik,
by permission of Gustav
Fischer.

Fig. 77.—Tetradynamous
stamens
(four long and two
short) of wallflower
(Cheiranthus Cheiri).

Fig. 78.

Fig. 79.

Fig. 80.

Fig. 78.—Pollinia, or pollen-masses, with their retinacula (g) or
viscid matter attaching them at the base. The pollen masses (p)
are supported on stalks or caudicles (c). These masses are easily
detached by the agency of insects. Much enlarged.

Fig. 79.—Pistil of Asclepias (a) with pollen-masses (p) adhering
to the stigma (s). b, pollen-masses, removed from the stigma, united
by a gland-like body. Enlarged.

The pollen-grains or microspores contained in the anther consist
of small cells, which are developed in the large thick-walled
mother-cells formed in the interior of the pollen-sacs (microsporangia)
of the young anther. These mother-cells are either
separated from one another and float in the granular fluid which
fills up the cavity of the pollen-sac, or are not so isolated. A
division takes place, by which four cells are formed in each, the
exact mode of division differing in dicotyledons and monocotyledons.
These cells are the pollen-grains. They increase
in size and acquire a cell-wall, which becomes differentiated into
an outer cuticular layer, or extine, and an inner layer, or intine.
Then the walls of the mother-cells are absorbed, and the pollen-grains
float freely in the fluid of the pollen-sacs, which gradually
disappears, and the mature grains form a powdery mass within
the anther. They then either remain united in fours, or multiples
of four, as in some acacias, Periploca graeca and Inga anomala,
or separate into individual grains, which by degrees become
mature pollen. Occasionally the membrane of the mother-cell is
not completely absorbed, and traces of it are detected in a
viscid matter surrounding the pollen-grains, as in Onagraceae.
In orchidaceous plants the pollen-grains are united into masses,
or pollinia (fig. 78), by means of viscid matter. In orchids each
of the pollen-masses has a prolongation or stalk (caudicle) which
adheres to a prolongation at the base of the anther (rostellum)
by means of a viscid gland (retinaculum) which is either naked
or covered. The term clinandrium is sometimes applied to the
part of the column in orchids where the stamens are situated.
In some orchids, as Cypripedium, the pollen has its ordinary
character of separate grains. The number of pollinia varies;
thus, in Orchis there are usually two, in Cattleya four, and in
Laelia eight. The two pollinia in Orchis Morio contain each
about 200 secondary smaller masses. These small masses, when
bruised, divide into grains which are united in fours. In Asclepiadaceae
the pollinia are usually united in pairs (fig. 79), belonging
to two contiguous anther-lobes—each pollen-mass having a
caudicular appendage, ending in a common gland, by means of
which they are attached to a process of the stigma. The pollinia
are also provided with an appendicular staminal covering (fig. 80).
The extine is a firm membrane, which
defines the figure of the pollen-grain, and
gives colour to it. It is either smooth, or
covered with numerous projections (fig. 81),
granules, points or crested reticulations.
The colour is generally yellow, and the surface
is often covered with a viscid or oily
matter. The intine is uniform in different
kinds of pollen, thin and transparent,
and possesses great power of extension.
In some aquatics, as Zostera, Zannichellia, Naias, &c., only one
covering exists.

Fig. 83.—Male flower of
Pellitory (Parietaria officinalis),
having four stamens with in-curved
elastic filaments, and
an abortive pistil in the centre.
When the perianth (p) expands,
the filaments are thrown
out with force as at a, so as to
scatter the pollen.

Fig. 82.—Germinating pollen-grain
of Epilobium (highly mag.)
bearing a pollen-tube s; e, exine;
i, intine; abc, the three spots
where the exine is thicker in
anticipation of the formation of
the pollen-tube developed in this
case at a.

Pollen-grains vary from 1/300 to 1/700 of an inch or less in diameter.
Their forms are various. The most common form of grain is
ellipsoidal, more or less narrow at the extremities, which are
called its poles, in contradistinction to a line equidistant from
the extremities, which is its equator. Pollen-grains are also
spherical; cylindrical and curved, as in Tradescantia virginica;
polyhedral in Dipsacaceae and Compositae; nearly triangular in
section in Proteaceae and Onagraceae (fig. 82). The surface of the
pollen-grain is either uniform and homogeneous, or it is marked
by folds formed by thinnings of the membrane. There are also
rounded portions of the membrane or pores visible in the pollen-grain;
these vary in number from one to fifty, and through one ​or more of them the pollen-tube is extended in germination of
the spore. In Monocotyledons, as in grasses, there is often only
one, while in Dicotyledons they number from three upwards;
when numerous, the pores are either scattered irregularly, or
in a regular order, frequently forming a circle round the equatorial
surface. Sometimes at the place where they exist, the outer
membrane, in place of being thin and transparent, is separated
in the form of a lid, thus becoming operculate, as in the passion-flower
and gourd. Within the pollen-grain is the granular
protoplasm with some oily particles, and occasionally starch.
Before leaving the pollen-sac a division takes place in the pollen-grain
into a vegetative cell or cells, from which the tube is
developed, and a generative cell, which ultimately divides to
form the male cells (see Angiosperms and Gymnosperms).

When the pollen-grains are ripe, the anther dehisces and the
pollen is shed. In order that fertilization may be effected the
pollen must be conveyed to the stigma of the pistil.
This process, termed pollination (see Pollination),
Pollination.
is promoted in various ways,—the whole form and
structure of the flower having relation to the process. In some
plants, as Kalmia and Pellitory (fig. 83), the mere elasticity
of the filaments is sufficient to effect this; in other plants
pollination is effected by the wind, as in most of our forest trees,
grasses, &c., and in such cases enormous quantities of pollen are
produced. These plants are anemophilous. But the common
agents for pollination are insects. To allure and attract them
to visit the flower the odoriferous secretions and gay colours
are developed, and the position and complicated structure of
the parts of the flower are adapted to the perfect performance
of the process. It is comparatively rare in hermaphrodite flowers
for self-fertilization to occur, and the various forms of dichogamy,
dimorphism and trimorphism are fitted to prevent this.

Fig. 84.—Flower of Tree
Paeony (Paeonia Moutan),
deprived of its corolla, and
showing the disk in the form
of a fleshy expansion (d)
covering the ovary.

Under the term disk is included every structure intervening
between the stamens and the pistil. It was to such structures
that the name of nectary was applied by old authors.
It presents great varieties of form, such as a ring, scales,
Disk.
glands, hairs, petaloid appendages, &c., and in the progress of
growth it often contains saccharine matter, thus becoming truly
nectariferous. The disk is frequently formed by degeneration
or transformation of the staminal row. It may consist of
processes rising from the torus, alternating with the stamens,
and thus representing an abortive whorl; or its parts may be
opposite to the stamens. In some
flowers, as Jatropha Curcas, in which
the stamens are not developed, their
place is occupied by glandular
bodies forming the disk. In Gesneraceae
and Cruciferae the disk consists
of tooth-like scales at the base
of the stamens. The parts composing
the disk sometimes unite and
form a glandular ring, as in the
orange; or they form a dark-red
lamina covering the pistil, as in
Paeonia Moutan (fig. 84); or a
waxy lining of the hollow receptacle,
as in the rose; or a swelling at the
top of the ovary, as in Umbelliferae,
in which the disk is said to be
epigynous. The enlarged torus
covering the ovary in Nymphaea
(Castalia) and Nelumbium may be regarded as a form of disk.

The pistil or gynoecium occupies the centre or apex of the
flower, and is surrounded by the stamens and floral envelopes
when these are present. It constitutes the innermost
whorl, which after flowering is changed into the fruit
The pistil.
and contains the seeds. It consists essentially of two parts, a
basal portion forming a chamber, the ovary, containing the ovules
attached to a part called the placenta, and an upper receptive
portion, the stigma, which is either seated on the ovary (sessile),
as in the tulip and poppy, or is elevated on a stalk called the
style, interposed between the ovary and stigma. The pistil
consists of one or more modified leaves, the carpels (or megasporophylls).
When a pistil consists of a single carpel it is simple or
monocarpellary (fig. 85). When it is composed of several carpels,
more or less united, it is compound or polycarpellary (fig. 86).
In the first-mentioned case the terms carpel and pistil are
synonymous. Each carpel has its own ovary, style (when
present), and stigma, and may be regarded as formed by a folded
leaf, the upper surface of which is turned inwards towards the
axis, and the lower outwards, while from its margins are developed
one or more ovules. This comparison is borne out by an examination
of the flower of the double-flowering cherry. In it no fruit
is produced, and the pistil consists merely of sessile leaves,
the limb of each being green and folded, with a narrow prolongation
upwards, as if from the midrib, and ending in a thickened
portion. In Cycas the carpels are ordinary leaves, with ovules
upon their margin.

From Strasburger’s
Lehrbuch der Botanik,
by permission of Gustav
Fischer.

Fig. 85.

Fig. 87.

Fig. 86.

Fig. 89.

Fig. 88.

Fig. 90.

Fig. 85.—Pistil of Broom (Cytisus) consisting of ovary o, style s,
and stigma t. It is formed by a single carpel.

Fig. 86.—Vertical section of the flower of Black Hellebore (Helleborusniger). The pistil is apocarpous, consisting of several distinct
carpels, each with ovary, style and stigma. The stamens are indefinite,
and are inserted below the pistil (hypogynous).

Fig. 87.—Fruit of the Strawberry (Fragaria vesca), consisting of
an enlarged succulent receptacle, bearing on its surface the small
dry seed-like fruits (achenes).

Fig. 89.—Pistil of Ranunculus. x, Receptacle with the points of
insertion of the stamens a, most of which have been removed.

Fig. 90.—Syncarpous Pistil of Flax (Linum), consisting of five
carpels, united by their ovaries, while their styles and stigmas are
separate.

A pistil is usually formed by more than one carpel. The carpels
may be arranged either at the same or nearly the same height
in a verticil, or at different heights in a spiral cycle. When they
remain separate and distinct, thus showing at once the composition
of the pistil, as in Caltha, Ranunculus, hellebore (fig. 86), and
Spiraea, the term apocarpous is applied. Thus, in Sedum (fig. 22)
the pistil consists of five verticillate carpels o, alternating with
the stamens e. In magnolia and Ranunculus (fig. 89) the separate
carpels are numerous and are arranged in a spiral cycle upon an
elongated axis or receptacle. In the raspberry the carpels are
on a conical receptacle; in the strawberry, on a swollen succulent
one (fig. 87); and in the rose (fig. 88), on a hollow one. When
the carpels are united, as in the pear, arbutus and chickweed,
the pistil becomes syncarpous. The number of carpels in a pistil
is indicated by the Greek numeral. A flower with a simple
pistil is monogynous; with two carpels, digynous; with three
carpels, trigynous, &c.

The union in a syncarpous pistil is not always complete;
it may take place by the ovaries alone, while the styles and
stigmas remain free (fig. 90), and in this case, when the ovaries
form apparently a single body, the organ receives the name of
compound ovary; or the union may take place by the ovaries
and styles while the stigmas are disunited; or by the stigmas ​and the summit of the style only. Various intermediate states
exist, such as partial union of the ovaries, as in the rue, where
they coalesce at their base; and partial union of the styles, as
in Malvaceae. The union is usually most complete at the base;
but in Labiatae the styles are united throughout their length, and
in Apocynaceae and Asclepiadaceae the stigmas only. When
the union is incomplete, the number of the parts of a compound
pistil may be determined by the number of styles and
stigmas; when complete, the external venation, the grooves
on the surface, and the internal divisions of the ovary indicate
the number.

Fig. 92.

Fig. 93.

Fig. 94.

Fig. 92.—Trilocular ovary of the Lily (Lilium), cut transversely.
s, Septum; o, ovules, which form a double row in the inner angle
of each chamber. Enlarged.

Fig. 93.—Diagrammatic section of a quinquelocular ovary, composed
of five carpels, the edges of which are folded inwards, and meet
in the centre forming the septa, s. The ovules (o) are attached to a
central placenta, formed by the union of the five ventral sutures.
Dorsal suture, l.

Fig. 94.—Diagrammatic section of a five-carpellary ovary, in
which the edges of the carpels, bearing the placentas and ovules o, are
not folded inwards. The placentas are parietal, and the ovules
appear sessile on the walls of the ovary. The ovary is unilocular.

Fig. 95.

Fig. 96.

Fig. 97.

Fig. 98.

Fig. 95.—Diagrammatic section of a five-carpellary ovary, in
which the septa (s) proceed inwards for a certain length, bearing the
placentas and ovules (o). In this case the ovary is unilocular, and the
placentas are parietal. Dorsal suture, l.

Fig. 97.—Transverse section of the fruit of the Melon (Cucumis
Melo), showing the placentas with the seeds attached to them. The
three carpels forming the pepo are separated by partitions. From
the centre, processes go to circumference, ending in curved placentas
bearing the ovules.

Fig. 98.—Diagrammatic section of a compound unilocular ovary,
in which there are no indications of partitions. The ovules (o) are
attached to a free central placenta, which has no connexion with
the walls of the ovary.

Fig. 91.—Pistil of Pea
after fertilization of the
ovules, developing to form
the fruit. f, Funicle or
stalk of ovule (ov); pl, placenta;
s, withered style and
stigma; c, persistent calyx.

Fig. 100.—The same cut horizontally,
and the halves separated
so as to show the interior of the
cavity of the ovary o, with the free
central placenta p, covered with
ovules g.

The ovules are attached to the placenta, which consists of a
mass of cellular tissue, through which the nourishing vessels
pass to the ovule. The placenta is usually formed on
the edges of the carpellary leaf (fig. 91)—marginal.
The placenta.
In many cases, however, the placentas are formations
from the axis (axile), and are not connected with the carpellary
leaves. In marginal placentation the part of the carpel bearing
the placenta is the inner or ventralsuture, corresponding to the margin
of the folded carpellary leaf, while
the outer or dorsal suture corresponds
to the midrib of the carpellary leaf.
As the placenta is formed on each
margin of the carpel it is essentially
double. This is seen in cases where
the margins of the carpel do not
unite, but remain separate, and consequently
two placentas are formed in
place of one. When the pistil is
formed by one carpel the inner margins
unite and form usually a common
marginal placenta, which may extend
along the whole margin of the ovary
as far as the base of the style (fig. 91),
or may be confined to the base or
apex only. When the pistil consists
of several separate carpels, or is
apocarpous, there are generally separate
placentas at each of their margins. In a syncarpous pistil,
on the other hand, the carpels are so united that the edges of
each of the contiguous ones, by their union, form a septum or
dissepiment, and the number of these septa consequently indicates
the number of carpels in the compound pistil (fig. 92). When the
dissepiments extend to the centre or axis, the ovary is divided
into cavities or cells, and it may be bilocular, triloculur (fig. 92),
quadrilocular, quinquelocular, or multilocular, according as it is
formed by two, three, four, five or many carpels, each carpel
corresponding to a single cell. In these cases the marginal
placentas meet in the axis, and unite so as to form a single central
one (figs. 92, 93), and the ovules appear in the central angle of
the loculi. When the carpels in a syncarpous pistil do not fold
inwards so that the placentas appear as projections on the walls
of the ovary, then the ovary is unilocular (fig. 95) and the
placentas are parietal, as in Viola (fig. 96). In these instances
the placentas may be formed at the margin of the united contiguous
leaves, so as to appear single, or the margins may not be
united, each developing a placenta. Frequently the margins of
the carpels, which fold in to the centre, split there into two
lamellae, each of which is curved outwards and projects into the
loculament, dilating at the end into a placenta. This is well
seen in Cucurbitaceae (fig. 97), Pyrola, &c. The carpellary leaves
may fold inwards very slightly, or they may be applied in a
valvate manner, merely touching at their margins, the placentas
then being parietal (fig. 94), and appearing as lines or thickenings
along the walls. Cases occur, however, in which the placentas
are not connected with the
walls of the ovary, and form
what is called a free centralplacenta (fig. 98). This is seen
in many of the Caryophyllaceae
and Primulaceae (figs.
99, 100). In Caryophyllaceae,
however, while the placenta
is free in the centre, there are
often traces found at the base
of the ovary of the remains of
septa, as if rupture had taken
place, and, in rare instances,
ovules are found on the
margins of the carpels. But
in Primulaceae no vestiges of
septa or marginal ovules can
be perceived at any period of
growth; the placenta is
always free, and rises in the
centre of the ovary. Free
central placentation, therefore,
has been accounted for in two ways: either by supposing
that the placentas in the early state were formed on the margins of ​carpellary leaves, and that in the progress of development these
leaves separated from them, leaving the placentas and ovules
free in the centre; or by supposing that the placentas are not
marginal but axile formations, produced by an elongation of the
axis, and the carpels verticillate leaves, united together around
the axis. The first of these views applies to Caryophyllaceae,
the second to Primulaceae.

Occasionally, divisions take place in ovaries which are not
formed by the edges of contiguous carpels. These are called
spurious dissepiments. They are often horizontal, as in CathartocarpusFistula, where they consist of transverse cellular prolongations
from the walls of the ovary, only developed after
fertilization, and therefore more properly noticed under fruit.
At other times they are vertical, as in Datura, where the ovary,
in place of being two-celled, becomes four-celled; in Cruciferae,
where the prolongation of the placentas forms a vertical partition;
in Astragalus and Thespesia, where the dorsal suture is folded
inwards; and in Oxytropis, where the ventral suture is folded
inwards.

The ovary is usually of a more or less spherical or curved form,
sometimes smooth and uniform on its surface, at other times
hairy and grooved. The grooves usually indicate the divisions
between the carpels and correspond to the dissepiments. The
dorsal suture may be marked by a slight projection or by a
superficial groove. When the ovary is situated on the centre
of the receptacle, free from the other whorls, so that its base is
above the insertion of the stamens, it is termed superior, as in
Lychnis, Primula (fig. 61) and Peony (fig. 64) (see also fig. 28).
When the margin of the receptacle is prolonged upwards, carrying
with it the floral envelopes and staminal leaves, the basal portion
of the ovary being formed by the receptacle, and the carpellary
leaves alone closing in the apex, the ovary is inferior, as in
pomegranate, aralia (fig. 65), gooseberry and fuchsia (see
fig. 30). In some plants,
as many Saxifragaceae,
there are intermediate
forms, in which the term
half-inferior is applied to
the ovary, whilst the
floral whorls are half-superior.

The style proceeds
from the summit of the
carpel (fig.
102), and is
traversed by a narrow
canal, in which there are
some loose projecting
cells, a continuation of
the placenta, constituting
what is called conducting
tissue, which ends in
the stigma. This is particularly
abundant when
The style.
the pistil is ready for
fertilization. In some
cases, owing to more
rapid growth of the
dorsal side of the ovary,
the style becomes lateral
(fig. 101); this may so
increase that the style
appears to arise from
near the base, as in the
strawberry, or from the base, as in Chrysobalanus Icaco, when
it is called basilar. In all these cases the style still indicates
the organic apex of the ovary, although it may not be the
apparent apex. When in a compound pistil the style of each
carpel is thus displaced, it appears as if the ovary were
depressed in the centre, and the style rising from the depression
in the midst of the carpels seems to come from the torus.
Such a style is gynobasic, and is well seen in Boraginaceae.
The form of the style is usually cylindrical, more or less filiform
and simple; sometimes it is grooved on one side, at other times
it is flat, thick, angular, compressed and even petaloid, as in Iris
(fig. 103) and Canna. In Goodeniaceae it ends in a cuplike
expansion, enclosing the stigma. It sometimes bears hairs,
which aid in the application of the pollen to the stigma, and are
called collecting hairs, as in Campanula, and also in Aster and other
Compositae. These hairs, during the upward growth of the
style, come into contact with the already ripened pollen, and
carry it up along with them, ready to be applied by insects to the
mature stigma of other flowers. In Vicia and Lobelia the hairs
frequently form a tuft below the stigma. The styles of a syncarpous
pistil are either separate or united; when separate, they
alternate with the septa; when united completely, the style is
said to be simple (fig. 102). The style of a single carpel, or of
each carpel of a compound pistil, may also be divided. Each
division of the tricarpellary ovary of Jatropha Curcas has a
bifurcate or forked style, and the ovary of Emblica officinalis has
three styles, each of which is twice forked. The length of the
style is determined by the relation which should subsist between
the position of the stigma and that of the anthers, so as to allow
the proper application of the pollen. The style is deciduous or
persists after fertilization.

The stigma is the termination of the conducting tissue of the
style, and is usually in direct communication with the placenta.
It consists of loose cellular tissue, and secretes a viscid
matter which detains the pollen, and causes it to
The stigma.
germinate. This secreting portion is, strictly speaking,
the true stigma, but the name is generally applied to all the
divisions of the style on which the stigmatic apparatus is situated.
The stigma alternates with the dissepiments of a syncarpous
pistil, or, in other words, corresponds with the back of the
loculaments; but in some cases it would appear that half the
stigma of one carpel unites with half that of the contiguous
carpel, and thus the stigma is opposite the dissepiments, that is,
alternates with the loculaments, as in the poppy.

Fig. 105.—Flower of a grass
with glumes removed, showing
three stamens and two
feathery styles. p, Pale; l,
lodicules. Enlarged.

The divisions of the stigma mark the number of carpels which
compose the pistil. Thus in Campanula a five-cleft stigma
indicates five carpels; in Bignoniaceae, Scrophulariaceae and
Acanthaceae, the two-lobed or bilamellar stigma indicates a
bilocular ovary. Sometimes, however, as in Gramineae, the
stigma of a single carpel divides. Its position may be terminal
or lateral. In Iris it is situated on a cleft on the back of the
petaloid divisions of the style (fig. 103). Some stigmas, as
those of Mimulus, present sensitive flattened laminae, which
close when touched. The stigma presents various forms. It may
be globular, as in Mirabilis Jalapa; orbicular, as in ArbutusAndrachne; umbrella-like, as in
Sarracenia, where, however, the
proper stigmatic surface is beneath
the angles of the large expansion
of the apex of the style; ovoid, as
in fuchsia; hemispherical; polyhedral;
radiating, as in the poppy
(fig. 104), where the true stigmatic
rays are attached to a sort of peltate
or shield-like body, which may
represent depressed or flattened
styles; cucullate, i.e. covered by a
hood, in calabar bean. The lobes
of a stigma are flat and pointed as
in Mimulus and Bignonia, fleshy
and blunt, smooth or granular, or
they are feathery, as in many
grasses (fig. 105) and other wind-pollinated
flowers. In Orchidaceae
the stigma is situated on the anterior surface of the column
beneath the anther. In Asclepiadaceae the stigmas are
united to the face of the anthers, and along with them form
a solid mass.

The ovule is attached to the placenta, and destined to become
the seed. Ovules are most usually produced on the margins of ​the carpellary leaves, but are also formed over the whole
surface of the leaf, as in Butomus. In other instances they rise
The ovule.
from the floral axis itself, either terminal, as in Polygonaceae
and Piperaceae, or lateral, as in Primulaceae
and Compositae. The ovule is usually contained in an ovary,
and all plants in which the ovule is so enclosed are termed
angiospermous; but in Coniferae and Cycadaceae it has no
proper ovarian covering, and is called naked, these orders being
denominated gymnospermous. In Cycas the altered leaf, upon
the margin of which the ovule is produced, and the peltate scales,
from which they are pendulous in Zamia, are regarded by all
botanists as carpellary leaves. As for the Coniferae great discussion
has arisen regarding the morphology of parts in many
genera. The carpellary leaves are sometimes united in such a
way as to leave an opening at the apex of the pistil, so that the
ovules are exposed, as in mignonette. In Leontice thalictroides
(Blue Cohosh), species of Ophiopogon, Peliosanthes and Stateria,
the ovary ruptures immediately after flowering, and the ovules
are exposed; and in species of Cuphea the placenta ultimately
bursts through the ovary and corolla, and becomes erect, bearing
the exposed ovules. The ovule is attached to the placenta either
directly, when it is sessile, or by means of a prolongation funicle
(fig. 110, f). This cord sometimes becomes much elongated after
fertilization. The part by which the ovule is attached to the
placenta or cord is its base or hilum, the opposite extremity being
its apex. The latter is frequently turned round in such a way
as to approach the base. The ovule is sometimes embedded in
the placenta, as in Hydnora.

Fig. 106.

Fig. 107.

Fig. 108.

Fig. 109.

Figs. 106 and 107.—Successive stages in the development of an
ovule. n, Nucellus; i, inner; o, outer integument in section; m,
micropyle.

Fig. 108.—Orthotropous ovule of Polygonum in section, showing
the embryo-sac s, in the nucellus n, the different ovular coverings,
the base of the nucellus or chalaza ch, and the apex of the ovule with
its micropyle m.

Fig. 109.—Vertical section of the ovule of the Austrian Pine
(Pinus austriaca), showing the nucellus a, consisting of delicate
cellular tissue containing deep in its substance an embryo-sac b.
The micropyle m is very wide.

The ovule appears at first as a small cellular projection from
the placenta. The cells multiply until they assume a more or
less enlarged ovate form constituting what has been called the
nucellus (fig. 106, n), or central cellular mass of the ovule. This
nucellus may remain naked, and alone form the ovule, as in
some orders of parasitic plants such as Balanophoraceae, Santalaceae,
&c.; but in most plants it becomes surrounded by certain
coverings or integuments during its development. These appear
first in the form of cellular rings at the base of the nucellus,
which gradually spread over its surface (figs. 106, 107). In some
cases only one covering is formed, especially amongst gamopetalous
dicotyledons, as in Compositae, Campanulaceae, also
in walnut, &c. But usually besides the single covering another
is developed subsequently (fig. 106, o), which gradually extends
over that first formed, and ultimately covers it completely,
except at the apex. There are thus two integuments to the
nucellus, an outer and an inner. The integuments do not
completely invest the apex of the nucellus, but an opening termed
the micropyle is left. The micropyle indicates the organic apex
of the ovule. A single cell of the nucellus enlarges greatly to
form the embryo-sac or megaspore (fig. 108, s). This embryo-sac
increases in size, gradually supplanting the cellular tissue of the
nucellus until it is surrounded only by a thin layer of it; or it
may actually extend at the apex beyond it, as in Phaseolus
and Alsine media; or it may pass into the micropyle, as in
Santalum. In Gymnosperms it usually remains deep in the
nucellus and surrounded by a thick mass of cellular tissue (fig.
109). For an account of the further development of the megaspore,
and the formation of the egg-cell, from which after fertilization
is formed the embryo, see Gymnosperms and Angiosperms.

Fig. 110.

Fig. 111.

Fig. 110.—Campylotropous ovule of
wall-flower (Cheiranthus), showing the
funicle f, which attaches the ovule to the
placenta; p, the outer, s, the inner coat,
n, the nucellus, ch, the chalaza. The
ovule is curved upon itself, so that the
micropyle is near the funicle.

Fig. 111.—Anatropous ovule of Dandelion
(Taraxacum), n, nucellus, which is
inverted, so that the chalaza ch, is removed
from the base or hilum h, while
the micropyle f is near the base. The
connexion between the base of the ovule
and the base of the nucellus is kept up
by means of the raphe r.

The point where the integuments are united to the base of
the nucellus is called the chalaza (figs. 111, 112). This is often
coloured, is of a denser
texture than the surrounding
tissue, and is
traversed by fibro-vascular
bundles, which
pass from the placenta
to nourish the ovule.

When the ovule is
so developed that the
chalaza is at the
hilum (next the placenta),
and the micropyle
is at the opposite
extremity, there being
a short funicle, the
ovule is orthotropous.
This form is well seen in
Polygonaceae (fig. 112),
Cistaceae, and most
gymnosperms. In such
an ovule a straight line
drawn from the hilum
to the micropyle passes
along the axis of the
ovule. Where, by more rapid growth on one side than on the
other, the nucellus, together with the integuments, is curved upon
itself, so that the micropyle approaches the hilum, and ultimately
is placed close to it, while the chalaza is at the hilum, the ovule is
campylotropous (fig. 110). Curved ovules are found in Cruciferae,
and Caryophyllaceae. The inverted or anatropous ovule (fig. 111)
is the commonest form amongst angiosperms. In this ovule the
apex with the micropyle is turned towards the point of attachment
of the funicle to the placenta, the chalaza being situated
at the opposite extremity; and the funicle, which runs along the
side usually next the placenta, coalesces with the ovule and
constitutes the raphe (r), which often forms a ridge. The
anatropous ovule arises from the placenta as a straight or only
slightly curved cellular process, and as it grows, gradually
becomes inverted, curving from the point of origin of the integuments
(cf. figs. 106, 107). As the first integument grows round
it, the amount of inversion increases, and the funicle becomes
adherent to the side of the nucellus. Then if a second integument
be formed it covers all the free part of the ovule, but does not
form on the side to which the raphe is adherent. These may be
taken as the three types of ovule; but there are various intermediate
forms, such as semi-anatropous and others.

The position of the ovule relative to the ovary varies. When
there is a single ovule, with its axis vertical, it may be attached
to the placenta at the base of the ovary (basal placenta), and is
then erect, as in Polygonaceae and Compositae; or it may be
inserted a little above the base, on a parietal placenta, with its
apex upwards, and then is ascending, as in Parietaria. It may
hang from an apicilar placenta at the summit of the ovary, its
apex being directed downwards, and is inverted or pendulous,
as in Hippuris vulgaris; or from a parietal placenta near the
summit, and then is suspended, as in Daphne Mezereum, Polygalaceae
and Euphorbiaceae. Sometimes a long funicle arises
from a basal placenta, reaches the summit of the ovary, and
there bending over suspends the ovule, as in Armeria (sea-pink);
at other times the hilum appears to be in the middle, and the
ovule becomes horizontal. When there are two ovules in the
same cell, they may be either collateral, that is, placed side by ​side (fig. 92), or the one may be erect and the other inverted,
as in some species of Spiraea and Aesculus; or they may be
placed one above another, each directed similarly, as is the case
in ovaries containing a moderate or definite number of ovules.
Thus, in the ovary of Leguminous plants (fig. 91), the ovules, o,
are attached to the extended marginal placenta, one above the
other, forming usually two parallel rows corresponding to each
margin of the carpel. When the ovules are definite (i.e. are
uniform, and can be counted), it is usual to find their attachment
so constant as to afford good characters for classification. When
the ovules are very numerous (indefinite), while at the same time
the placenta is not much developed, their position exhibits great
variation, some being directed upwards, others downwards,
others transversely; and their form is altered by pressure into
various polyhedral shapes. In such cases it frequently happens
that some of the ovules are arrested in their development and
become abortive.

From Strasburger’s Lehrbuch derBotanik, by permission of Gustav Fischer.

Fig. 113.—Vertical section of
the ovule of the Scotch Fir (Pinussylvestris) in May of the second
year, showing the enlarged embryo-sac
b, full of endosperm
cells, and pollen-tubes c, penetrating
the summit of the nucellus
after the pollen has entered the
large micropyle.

When the pistil has reached a certain stage in growth it becomes
ready for fertilization. Pollination having been effected, and
the pollen-grain having reached the stigma in angiosperms,
or the summit of the nucellus in gymnosperms,
Fertilization.
it is detained there, and the viscid secretion from the
glands of the stigma in the former case, or from the nucellus in
the latter, induce the protrusion of the intine as a pollen-tube
through the pores of the grain.
The pollen-tube or tubes pass
down the canal (fig. 112),
through the conducting tissue
of the style when present, and
reach the interior of the ovary
in angiosperms, and then pass
to the micropyle of the ovule,
one pollen-tube going to each
ovule. Sometimes the micropyle
lies close to the base of
the style, and then the pollen-tube
enters it at once, but
frequently it has to pass some
distance into the ovary, being
guided in its direction by various
contrivances, as hairs,
grooves, &c. In gymnosperms
the pollen-grain resting on the
apex of the nucellus sends out
its pollen-tubes, which at once
penetrate the nucellus (fig. 113).
In angiosperms when the pollen-tube
reaches the micropyle it
passes down into the canal, and this portion of it increases
considerably in size. Ultimately the apex of the tube comes in
contact with the tip of the embryo-sac and perforates it. The
male cells in the end of the pollen-tube are then transmitted to
the embryo-sac and fertilization is effected. Consequent upon
this, after a longer or shorter period, those changes commence
in the embryo-sac which result in the formation of the embryo
plant, the ovule also undergoing changes which convert it into
the seed, and fit it for a protective covering, and a store of
nutriment for the embryo. Nor are the effects of fertilization
confined to the ovule; they extend to other parts of the plant.
The ovary enlarges, and, with the seeds enclosed, constitutes
the fruit, frequently incorporated with which are other parts
of the flower, as receptacle, calyx, &c. In gymnosperms the
pollen-tubes, having penetrated a certain distance down the
tissue of the nucellus, are usually arrested in growth for a longer
or shorter period, sometimes nearly a year. Fruit and seed are
discussed in a separate article—Fruit.
(A. B. R.)